Spectral imaging of substrates

ABSTRACT

Spectral imaging systems and methods are provided for monitoring a substrate during a chemical-mechanical planarization process. An example system includes a carrier configured to receive a substrate, and a platen configured to receive a polishing pad. The platen includes an aperture configured to pass light. The system also includes a frame that disposes the platen in any number of positions relative to the carrier. An optoelectronic system is coupled to the aperture, and the aperture passes light of the optoelectronic system to illuminate the substrate and passes reflected light from the substrate to the optoelectronic system. A processing system is coupled to the optoelectronic system and uses the reflected light to image the substrate as the polishing pad is polishing the substrate.

RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application No. 60/638,660, filed Dec. 23, 2004, and is a continuation-in-part application of U.S. patent application Ser. No. 10/815,555, filed Apr. 1, 2004.

FIELD OF THE INVENTION

The embodiments described herein relate to in situ metrology during chemical-mechanical planarization (CMP) and, more particularly, to monitoring a film on a substrate as it is planarized.

BACKGROUND OF THE INVENTION

Chemical-mechanical planarization (CMP) has emerged as a dominant technology for minimizing surface topology during the manufacture of integrated circuits. By minimizing surface topology, the entire surface can be arranged to be within the depth of field of lithography tools, which results in significantly reduced feature dimensions and a dramatic rise in the value of devices made with such features.

The basic concept of CMP is generally to press a substrate against a polish pad in the presence of a slurry and relative motion between the substrate and the polish pad. This combination causes “high” regions to abrade more quickly than “low” regions. Over time, the “high” regions are abraded away leaving a very flat surface. The flatness of such a surface depends in part on the composition of the substrate. If the substrate is completely homogeneous, then the surface can become extremely flat. However, if there are structures present in the substrate, such as metal lines embedded in a dielectric film (formed using a so-called damascene process), exposure of such metal lines during CMP can lead to significant variation in etch rate depending on the exposed materials.

CMP is used for planarizing both metal and dielectric film stacks. Examples of metal stacks include tungsten over titanium nitride over titanium, and copper over tantalum over tantalum nitride. Examples of dielectric film stacks include front-end of the line structures such as shallow trench isolation and back-end of the line inter-level dielectric films on top of metal lines.

Whether planarizing metal or dielectric stacks, the ability to monitor the polishing process and the ability to stop polishing at the appropriate time are critical aspects of quality control. If polishing a metal film, incomplete polishing results in regions of residual metal, which causes electrical shorts and device failures. Excessive polishing of metal films causes erosion of underlying dielectric layers, which can dramatically degrade device performance due to increased circuit capacitance. Likewise, incomplete or excessive dielectric planarization can also cause problems. Incomplete planarization results in excessive residual topology, which causes poor feature definition during lithographic exposures and therefore results in poor yield. Excessive planarization causes dishing and increased capacitance, which also degrades circuit performance. Differential material removal rates across a substrate being polished causes non-uniformity that also contributes to poor performance. Finally, the inability to compensate for overall substrate polish non-uniformity prevents optimum performance.

To overcome these limitations many techniques have been proposed to provide a stable CMP process. These techniques fall into two broad categories: local endpoint detection techniques and global endpoint detection techniques. Global endpoint detection systems measure a single aspect of a CMP process, and infer the condition of the substrate across the entire surface being polished. Repeated measurements provide a time dependent global signal representative of the progress of the polish process. The global endpoint detection techniques can provide an indication of the status of the polish process across the entire substrate. One such technique generates an endpoint signal by polishing a blank substrate, determining an etch rate, and then calculating a polish time based on a known thickness of film to be removed, and on the etch rate. However, this technique suffers from being susceptible to variations in the etch rate as the polish pad ages and wears out. Global endpoint detection also suffers from the lack of information about individual sites on the surface of the substrate during the polish process.

Local endpoint detection systems sense the surface of a small portion of a substrate during the polish process and infer global properties based on this measurement. Typically, such measurements involve multiple such measurements and result in some limited information about the condition of the substrate at the time of the measurement. For example, one technique uses a sensor that sweeps across a substrate and makes measurements to produce a diameter scan. However, this technique suffers from being unable to accurately infer the condition of the substrate across the entire surface being polished, i.e., where measurements are not being made.

Both local and global endpoint detection approaches can provide valuable information about the polish process. However, typical systems fail to offer the benefits of both types of systems.

Furthermore, as device geometries and edge exclusion zones (the un-usable periphery of a substrate) shrink, there is a growing need for detailed, quantitative information about the condition of all points on a substrate during the polish process, not just at the end of the polish process. Such information is essential not only for understanding how the polish process evolves, but more importantly for use in adjusting polish parameters during the polish process to optimize polish uniformity within a substrate and from substrate to substrate. One specific application involves multi-zone carriers. Such carriers apply differential pressure to different portions of the substrate to compensate for non-uniformities in the polish process, and require feedback to know how much pressure each zone should apply to produce an optimally polished substrate.

One example of a global endpoint technique for monitoring and controlling CMP processes measures the motor current of the carrier and platen used to cause relative motion between the substrate and the polish pad. U.S. Pat. No. 5,069,002 describes this global endpoint detection approach. As the material being polished clears and a different material is exposed, differences in friction cause a change in motor current that can be detected. This approach suffers from a dependence on polishing materials having very distinct friction against the polish pad being used. As a global endpoint detection technique, this approach provides no information about planarization at any particular location on a substrate being planarized.

Another proposed global endpoint detection technique involves measuring the capacitance of the wafer against the polish pad during the polish process, as described in U.S. Pat. No. 5,081,421. However, this approach typically depends strongly on the pattern of structures formed on substrates being polished. It has also involved a very poor signal to noise ratio, and provides no local polish process information.

Numerous approaches based on acoustical methods have also been proposed including those described in U.S. Pat. Nos. 5,876,265, 5,240,552, 5,245,794, 5,222,329, 5,399,234, and 5,196,006. These patents generally describe approaches that assess the overall surface of the substrate being polished, but suffer from being unable to provide locations specific process information. Thus, these approaches generally are not production worthy and require sophisticated expertise to use.

Numerous optically based techniques have also been proposed for monitoring in situ CMP process performance, and in particular for detecting endpoint during a CMP process. All of these techniques are local endpoint detection techniques and involve shining light at a substrate being planarized and monitoring either reflected or transmitted light. These techniques further involve sensing light reflected from one or more points on a wafer, and inferring endpoints based on these measurements. These techniques involve making measurements serially, and at one location at a time.

Several proposed techniques use single wavelength light, e.g. light from a laser source, and monitor the intensity of reflected light. One particular technique, described in U.S. Pat. No. 6,494,766, involves scanning a single light source across a wafer to obtain a plurality of measurements, partitioning these measurements into radial components, and inferring endpoint based on these measurements. Although this approach can provide a diameter scan, it suffers from providing no information about areas away from the diameter line being measured. This approach further suffers from an inability to detect whether a substrate has slipped during polish, which can be a serious process issue. Other techniques exploit the information available in a broad spectrum, e.g. visible light. However, all of these techniques provide limited information about the planarization process across the entire substrate.

An additional limitation of these optical techniques is that they are sensitive to signal noise created by light scattering from feature edges. Such diffraction effects are known to have both wavelength and angular dependence, and can substantially affect spectral profiles.

U.S. Pat. No. 5,949,927 describes a technique and apparatus for the optical monitoring and measurement of a thin film (or small region on a surface) undergoing thickness and other changes while it is rotating. As such, it is a local endpoint detection system. However, this technique does not seem to address the issue of assessing light scattered and/or diffracted from patterned features. The patent purports to allow measurements to be made on fixed, selected portions of a wafer, but does not describe how arbitrary, pre-determined site can be selected. Other optical endpoint patents, such as the abovementioned '766 patent suffer from the same limitation. Sites that do not pass over the fixed-location sensor cannot be measured. Furthermore, incidental substrate rotation during the polish process would cause measurements to be erroneous. Thus, global endpoint detection needs are again not addressed.

An additional challenge of optical endpoint detection systems relates to the multiplicity of film stacks likely to be present during CMP. Stationary metrology systems such as those manufactured by companies such as KLA-Tencor, Thermawave, and Rudolph Technologies address this issue by positioning each substrate on a vibrationally isolated platform, and focusing light to a spot as small as 10 micrometers. This combination ensures that sensed light corresponds to light reflected from a single film stack. Substrates being polished on CMP tools are in motion and immersed in slurry, which is translucent. The motion of the substrate causes light to scan across multiple film stacks, which significantly affects the measured spectral response and complicates signal analysis.

Developments have led to an increased need for precise control over the planarization process. The use of copper for increased conductivity of electrical interconnects requires the use of ultra-thin barrier metals. However, slurries suitable for planarizing copper do not work well on the barrier metals, so processes using multiple slurries have been developed. These processes require extremely precise control over when a first slurry is changed to a second slurry to avoid regions of un-cleared metal or regions of over-polished metal.

INCORPORATION BY REFERENCE

Each publication and/or patent application mentioned in this specification is herein incorporated by reference in its entirety to the same extent as if each individual publication and/or patent application was specifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of an imaging system on a CMP tool, under an embodiment.

FIG. 2A shows one embodiment of the surface of a platen with an aperture for viewing a substrate during polishing, under an embodiment.

FIG. 2B shows a schematic representation of a layout of components of an imaging system, under an embodiment.

FIG. 3 shows an alignment of a fiber assembly within the aperture of a platen for viewing a substrate during CMP, under an embodiment.

FIG. 4A shows a top view of the fiber assembly, under an embodiment.

FIG. 4B shows a detailed view of illumination and sensing fibers, under an embodiment.

FIG. 5 shows a line-scan spectrometer, under an embodiment.

FIGS. 6A-6E show a layout of illumination and sensing fibers of a fiber assembly, under an embodiment.

FIGS. 7A-7C show an alternate layout of illumination and sensing fibers of a fiber assembly, under an embodiment.

FIG. 8 is a flow diagram for acquiring and processing spectral reflectance data, under an embodiment.

FIGS. 9A-9C show system component of an embodiment during imaging operations.

FIG. 10 shows an image of a substrate during CMP, under an embodiment.

FIG. 11 shows an imaging system on a CMP tool, under an embodiment.

FIG. 12A shows a surface of a platen having an aperture for viewing a substrate during a CMP process, under an embodiment.

FIG. 12B is a schematic representation of one embodiment of a layout of components of a whole-die imaging system, under an embodiment.

FIG. 13 shows a swath corresponding to a die-sized optical assembly as it traverses a substrate, under an embodiment.

FIG. 14 is a flow diagram for acquiring and processing spectral reflectance data using an imaging system, under an embodiment.

FIG. 15A shows a swath of acquired data, under an embodiment.

FIG. 15B shows a die having an optical difference in a quadrant, under an embodiment.

FIG. 15C shows an intersection of a street and a transverse street with an optical difference in an adjacent die quadrant, under an embodiment.

FIGS. 16A-16C show line imaging spectrometers, under various alternative embodiments.

FIG. 17 shows an orbital CMP tool that includes an imaging system for in situ substrate monitoring, under an embodiment.

FIG. 18A shows a top view of a pad structure, under an embodiment.

FIG. 18B shows an example trajectory of a single point on the polish pad during orbital motion, under an embodiment.

FIG. 19 shows an image of a patterned substrate during orbital CMP, under an embodiment.

DETAILED DESCRIPTION

Spectral imaging (also referred to herein as “imaging”) is described below including systems and methods for monitoring a substrate during a chemical-mechanical planarization process. Example systems and methods under the spectral imaging include a carrier configured to receive a substrate, and a platen configured to receive a polishing pad. The platen includes an aperture configured to pass light. The system also includes a frame that disposes the platen in any number of positions relative to the carrier. An optoelectronic system is coupled to the aperture, and the aperture passes light of the optoelectronic system to illuminate the substrate and passes reflected light from the substrate to the optoelectronic system. A processing system is coupled to the optoelectronic system and uses the reflected light to image the substrate as the polishing pad is polishing the substrate.

In the following description, numerous specific details are introduced to provide a thorough understanding of, and enabling description for, embodiments of the imaging. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

An imaging system 105 is described herein that allows a substrate 180 to be monitored during a polish chemical-mechanical planarization process. Portions of the substrate 180 and/or the whole substrate 180 can be imaged by the imaging system 105 under various embodiments. FIG. 1 shows an imaging system 105 that includes a platen 120 with an aperture 130, a fiber assembly 125 disposed within aperture 130, and an optoelectronic assembly 115 that is optically coupled to fiber assembly 125 via illuminator bundle 174 and sensor bundle 172. The imaging system 105 further includes an electrical connector 176, a rotating coupler 110 and an electrical connector 177, which are electrically connected in series so that optoelectronic assembly 115 is electrically connected to a system controller 108. System controller 108 and electrical connector 177 are located remotely from platen 120 but are not so limited.

The imaging system 105 is used in a CMP tool 100 of an embodiment that further includes a polish pad 135 mounted on platen 120, a motor (not shown) that causes platen 120 to rotate about axis of rotation 150 at a platen rotation rate, a carrier assembly 170 rotated by a second motor (also not shown) about axis of rotation 155 at a carrier rotation rate. Axis of rotation 155 is offset from axis of rotation 150 by a distance R_(OFFSET), which may vary with time. Carrier assembly 170 includes a retaining ring 182 that secures substrate 180 in place during the polish process. A slurry delivery system (not shown) provides slurry to polish pad 135 near axis of rotation 150 so that centrifugal forces disperse the slurry over polish pad 135. A CMP system controller (not shown) controls the operation of the CMP tool.

Substrate 180 can include a semiconductor wafer having a center and a diameter with partially formed elements of an integrated circuit formed on one side. The partially formed elements include at least one film stack to be planarized. Example film stacks include without limitation copper with a tantalum under-layer, tungsten over titanium nitride over titanium, silicon dioxide, and spin-on-glass (SOG). Substrate 180 may be formed from materials such as silicon, gallium arsenide, gallium antimonide, or other III-V materials. Substrate 180 may also be formed from II-VI materials such as HgCdTe. In addition, substrate 180 may be formed of any of a wide variety of glasses such as BK7, flint glasses, and fused silica, or plastics such as polymethylacrylate, polycarbonate, etc. Substrate 180 may also include partially formed flat panel displays.

Platen 120 is a disk having a working face 122 with a radius that is larger than the diameter of substrate 180 in an embodiment. Platen 120 is a solid disk except for portions the disk that have been removed to accommodate the imaging system 105. However, it is not necessary that the disk be solid, and other configurations or arrangements such as a hollow disk or a thin, solid disk over a honeycomb core are included hereunder. Additionally, aperture 130, which is described herein as being cut into platen 120 in a generally rectangular form, is not restricted to a rectangular form. The aperture 130 or opening in platen 120 that can comprise any shape and/or configuration through which light may pass. The aperture 130 for example can include a slit 130 that passes light that illuminates substrate 180 and/or light reflected from substrate 180 for the purposes of capturing reflectance data from a substrate 180. Accordingly, aperture 130 can be rectangular, circular, oblong, symmetrical, asymmetrical, or any other shape as appropriate to particular embodiments.

Rotating coupler 110 provides for the exchange of electrical signals between optoelectronic assembly 115 and system controller 108. An example of the rotating coupler 110 is available as a Mercotac Connector from Mercotac, Inc. (Carlsbad, Calif.),

Electrical connector 176 and electrical connector 177 include conductors that deliver synchronization and control signals, as well as power, to optoelectronic assembly 115. The conductors can include wires, cables, fibers, and/or traces but are not so limited. Electrical connector 176 and electrical connector 177 further include conductors that deliver a video signal from optoelectronic assembly 115 to system controller 108.

Polish pad 135 includes an optical element (or window) 137 for passing or transmitting light, and attaches adhesively to working face 122 of platen 120. An example of polish pad 135 includes the IC1000 available from Rodel Corporation of Wilmington, Del. Window 137 is transparent, and in one embodiment, may be formed from JR111 material from Rodel Corp. In another embodiment, polish pad 135 may be transparent.

Optoelectronic assembly 115 generates light that propagates into illuminator bundle 174, and receives light from sensor bundle 172, which optoelectronic assembly 115 converts to an electrical signal. The electrical signal is directed to rotating connector 110 via electrical connector 176 for use by a system processor. This electrical signal can be structured to represent the image of substrate 180, or it can be structured to signal the CMP system controller to stop polishing or to go to the next polish step.

Illuminator bundle 174 is a bundle of optical fibers that couple light from optoelectronic assembly 115 to fiber assembly 125. Sensor bundle 172 is a bundle of optical fibers that couple light reflected from substrate 180 to optoelectronic assembly 115.

System controller 108 includes a processor and a video frame grabber, and interfaces with the CMP system controller. The CMP system controller provides information such as the rotation rate of platen 135, the rotation rate of carrier 170, and the distance of R_(OFFSET), to system controller 108. Based on this information, system controller 108 generates an angle reference signal used to allow optoelectronic assembly 115 to collect reflectance data when fiber assembly 125 is beneath carrier 170.

System controller 108 further includes a variable power supply controlled by the computer. The variable power supply may comprise a Schott-Fostec Model DCR® III (Schott-Foster, Auburn, N.Y.) illuminator for fiber optic cables, to which functionality of the light bulb has been removed to optoelectronic assembly 115 in platen 135. The variable power supply generates a power and control signal that is communicated to optoelectronic assembly 115 via connector 177, rotating coupler 110, and connector 176. The power and control signal has a voltage that varies through a range of approximately nine (9) to twenty-one (21) volts (V), and serves to provide power for optoelectronic assembly 115 and to regulate light generated by optoelectronic assembly 115.

In operation, a substrate 180 loaded into carrier assembly 170 is pressed into polish pad 135 while carrier assembly 170 rotates about axis of rotation 155, platen 120 rotates about axis of rotation 150, and slurry flows across polish pad 135. A combination of chemical and mechanical processes abrades material from the surface of substrate 180. While the polishing process takes place, optoelectronic assembly 115 generates light based on the power and control signal generated by the variable power supply generator within system controller 108. This light passes through optical illuminator bundle 174 to fiber assembly 125, where it illuminates wafer 180 as aperture 130 passes under wafer 180. Fiber assembly 125 also receives light reflected from wafer 180, and directs this reflected light into sensor bundle 172. Optoelectronic assembly 115 receives the reflected light and converts it into the video signal than can be converted into an image of substrate 180 by system controller 108.

FIG. 2A shows a schematic representation of working face 122 of platen 120, and the position of fiber assembly 125 in aperture 130. FIG. 2B shows a schematic representation of optoelectronic assembly 115 within platen 120. Optoelectronic assembly 115 includes a controller 195, a light source 160, a spectrometer 190, connector 182, and connector 184.

Aperture 130 extends from near rotational coupler 110 radially outward. Aperture 130 is longer than the diameter of substrate 180, and allows R_(OFFSET) to be varied to meet CMP process requirements. Aperture 130 is approximately 2 millimeters (mm) wide in an embodiment, but only needs to be wide enough to allow light from the illumination fibers and to the sensors fibers to pass unobstructed. Aperture 130 of an embodiment should be at least as long as the wafer diameter plus any required additional length to accommodate wafer misplacement or motion associated with R_(OFFSET), but may not be so limited. Aperture 130 may optionally include a transparent platen window, or transparent element, to ensure fluids do not interfere with the functionality of optoelectronic assembly 115.

Controller 195 provides an interface between system controller 108 and spectrometer 190 and light source 160. Controller 195 is operatively coupled or connected to light source 160 via connector 182, which allows controller 195 to control light source 160. Controller 195 is also operatively coupled or connected to spectrometer 190 via connector 184. Controller 195 interprets the power and control signal from the variable power supply in system controller 108 as an ON/OFF and/or intensity control for light source 160. In one embodiment, if the voltage of the power and control signal drops below 10 V, it is interpreted as being in an OFF state, and if the voltage is greater than 10 V, the light is turned on to an intensity proportional to the voltage in excess of 10 V. Controller 195 further uses the power and control signal to provide power for spectrometer 190 using a direct current (DC)-DC converter (not shown). The functionality of controller 195 can be implemented using standard electronic components and design techniques known in the art.

Light source 160 includes a 150 watt (W) EKE bulb but is not so limited. A representative 150 W EKE bulb is available from Schott Fostec of Auburn, N.Y. Light source 160 emits light in a wavelength range from approximately 400 nm to 800 nm. Alternative embodiments hereunder can include a light source 160 that is a multiple wavelength source that emits at light at least two discrete wavelengths. Further, light source 160 can include a single wavelength emitting source such as a laser, provided the light emitted by the laser is not strongly absorbed by the slurry used to polish substrate 180.

Spectrometer 190 includes a wavelength-dispersive element, such as a prism or diffraction grating that separates light reflected from substrate 180 and passed through sensor bundle 172 into its spectral components. Spectrometer 190 converts these spectral components into a video signal that is communicated to system controller 108 via connector 176, rotational coupler 110 and connector 177.

Sensor bundle 172 is further described as including a plurality of fibers, each having a sensing end and an emitting end arranged so that the sensing ends are disposed within fiber assembly 125 so that as substrate 180 passes over aperture 130, each sensing end sweeps across substrate 180 such that the ensemble of sensing ends sweep over the entirety of substrate 180. Thus, the sensing ends form an array of data collection locations. In one embodiment, this array is disposed substantially non-parallel to the direction of substrate motion.

FIG. 3 shows a simplified cross-sectional view of fiber assembly 125 prior to it being inserted into aperture 130. Fiber assembly 125 has a nominally rectangular cross section with an active face 127 whose adjacent longitudinal edges are beveled to an angle α. The beveled edged serves to position fiber assembly 125 in aperture 130 for example. Face 127 may optionally comprise the optically transparent element 137 for allowing passage of light, whether reflected from the pad-contacting surface through element 137 to sensor bundle 172, or transmitted through element 137 from illuminator bundle 174. Transparent element 137 may be integral to fiber assembly 125, or it may be located elsewhere about the aperture. Element 137 may comprise glass, plastic, water, an air gap, and/or any other transparent fluid and/or material appropriate to the configuration. In other embodiments, element 137 may be integral to, or comprise in whole or in part, platen 120 or polish pad 135. For example, the embodiment of FIG. 3 shows polish pad 135 having element 137 in the form of a rectangular window formed therein so that element 137 is aligned with aperture 130.

Although illuminator bundle 174 includes many fibers, FIG. 3 shows only two representative illumination fibers, illumination fiber 310 a with termination end 194 a and illumination fiber 330 a with termination end 194 b. Likewise, sensor bundle 172 includes many sensor fibers, but FIG. 3 shows a single representative sensor fiber, sensor fiber 320 a, which has a termination end 192 a. Illumination fiber 310 a and illumination fiber 330 a extend from illuminator bundle 174 to face 127 of fiber assembly 125. Likewise, sensor fiber 320 a extends from sensor bundle 172 to face 127 of fiber assembly 125. Termination end 192 a is disposed between termination end 194 a and termination end 194 b.

In operation, light from light source 160 propagates through illumination fiber 310 a in illuminator bundle 174 to termination end 194 a and through illumination fiber 330 a to termination end 194 b, and is emitted from face 127 of fiber assembly 125. Some of the light reflected from substrate 180 enters sensor fiber 320 a through termination end 192 a, which directs the light back to spectrometer 190 via sensor bundle 172.

FIG. 4A shows a top view of fiber assembly 125 (not to scale). Fiber assembly 125 has a length and a width, with the length being slightly longer than the diameter of substrate 180, e.g. 220 mm if designed for use with 200 mm wafers. The width is typically in a range of approximately one (1) to five (5) millimeters. Illuminator bundle 174 couples or connects to one side of the long dimension of fiber assembly 125 and sensor bundle 172 couples or connects to the opposing side. FIG. 4 further shows a row of sensor fibers 320 disposed between a first row of illumination fibers 310 and a second row of illumination fibers 330.

Illumination fibers 310 and illumination fibers 330 are optical fibers. In an embodiment, the fibers are plastic with a diameter of approximately 0.75 mm, but fibers having diameters ranging from approximately 1 mm to approximately 0.05 mm can also be used.

Sensor fibers 320 are optical fibers with a diameter of approximately 0.100 mm and with a termination end having an area. Fibers with a larger diameter can also be used. Fibers with a smaller diameter can also be used to increase spatial resolution.

With continuing reference to FIG. 4A, illumination fibers 310 and illumination fibers 330 are oriented edge-to-edge along a straight line with a center-to-center spacing approximately equal to the fiber diameter. A distance approximately equal to the radius of the illumination fibers separates illumination fibers 310 and illumination fibers 330.

Illuminator bundle 174 includes several hundred fibers per row of fibers. The number of rows of illumination fibers 310 times the thickness of the individual illumination fibers should be approximately 1 mm or larger. Likewise, the number of rows of illumination fibers 330 times the thickness of the individual illumination fibers should be approximately 1 mm or larger. By way of example, illuminator bundle 174 requires approximately 300 fibers per row of fibers if the fibers have a diameter of 0.75 mm and are arranged edge-to-edge as shown in FIG. 4A. Thus, with two rows of illumination fibers, illuminator bundle 174 requires a total of 600 fibers. Examples of illumination fiber configurations that work include a single row of fibers having a thickness of 0.75 mm, two rows of fibers having a thickness of 0.50 mm, and five rows of fibers having a thickness of 0.20 mm. The number of illumination fibers 310 and illumination fibers 330 depends on the desired resolution of the image formed under an embodiment. The resolution is also affected by the amount of light available to illuminate substrate 180, and by the rotation rates of carrier 170 and of platen 120, and to a lesser extent by R_(OFFSET). By way of example, a configuration involves approximately 600 illumination fibers and 300 sensor fibers with terminations 192 a distributed along an overall length of 220 mm, but is not so limited.

Sensor fibers 320 are on centers approximately equal to the desired resolution of the final wafer image. Overall image resolution depends in part on the number of sensor fibers 320 used to form sensor bundle 172. Increasing the number of sensor fibers increases resolution. In one embodiment, 300 sensor fibers 320 are used.

Sensor fibers 320 collect light from a cone having an apex at the termination end of each sensor fiber, and extending through window 137 in pad 135 to substrate 180. This cone has a numerical aperture (NA) of approximately 0.22, and forms a detection spot approximately 1 mm in diameter on substrate 180. Since measurements are made during an integration time and while substrate 180 is moving relative to sensor fibers 320, the actual area on substrate 180 that is being sensed is oblong, and is approximately 1.5 mm long. This portion of the substrate is sensed by light reflected from the detection spots corresponding to each sensor fiber, thereby providing a spatial field of detection spots that form a one-dimensional reflectance image. Thus, in one embodiment, data point spacing may be provided by the spatial field of detection spots the imaging system. The detection spots, and/or data points, may be spaced in an array that is substantially contiguous, or substantially non-contiguous. A substantially contiguous array of data points is one derived from an array of detection spots on a substrate 180 whereby a substantial number of adjacent detection spots touch at their borders, or overlap, such that a continuous, or nearly continuous image of an illuminated portion of the substrate may be detected. A substantially non-contiguous array of data points is one that is not substantially contiguous, i.e. one derived from an array of detection points where substantial pairs of adjacent detection points on a substrate 180 are separated, leaving some portion of the illuminated substrate undetected.

FIG. 4B shows a location of sensor fibers 320 with respect to illumination fibers, under an embodiment. By way of example, FIG. 4B shows representative illumination fiber 310 a and illumination fiber 310 b positioned side-by-side and opposed by illumination fiber 330 a and illumination fiber 330 b. Sensor fiber 320 a is disposed between illumination fibers 310 a and 310 b and illumination fibers 330 a and 330 b.

Illumination fibers 310 and illumination fibers 330 serve several purposes. The illumination fibers 310 and 330 provide a conduit for delivering sufficient light to substrate 180 that the light collected by sensor fibers 320 can be analyzed easily. By providing multiple light sources for each individual sensor fiber, and in particular distributed light around each sensor fiber 320 a as shown in FIG. 4B, any angular dependence of light sensed by the sensor fibers is averaged out. Further, by providing illumination sources that are individually large compared to the size of the sensor fibers, any azimuthal dependence of light sensed by the sensor fibers is also averaged out. This combination reduces or minimizes the effect of light diffracting off structures in the surface of substrate 180.

The relatively large diameter of illumination fibers serves to provide a large area illumination source that suppresses diffractive effects when light scatters from device features on substrate 180. Further, the amount of light collected by sensor fibers 320 depends in part on the distance between the sensor fiber termination (e.g. termination 192 a) and substrate 180. This distance corresponds to the thickness of polish pad 135, which diminishes during polish. New polish pads have a thickness of approximately 2.4 mm, and are replaced when the polish pad thickness is approximately 1.5 mm. Each sensor fiber 192 a receives light emitted from illumination fibers 310 a, 310 b, 330 a, and 330 b. By arranging for light to strike substrate 180 over an area large compared to the area of sensor fiber termination 192 a, the light source behaves as an extended source regardless of the change in thickness of polish pad 135.

In operation, illumination fibers 310 and illumination fibers 330 emit light out of fiber assembly 125 and onto substrate 180. Some of the light reflected by substrate 180 enters sensor fibers 320, and propagates to spectrometer 190, which analyzes it.

FIG. 5 shows a line imaging spectrometer 511 that is part of spectrometer 190. Line imaging spectrometer 511 comprises a lens assembly 560, a diffraction grating 570, and a two-dimensional imager 580. The line imaging spectrometer 511 operates as follows. Light from source 160 passes through illumination bundle 174, and impinges on a film contained on or in substrate 180. The light reflects off the wafer and is received by sensor bundle 172, which couples the light to lens assembly 560 that produces a line image of a corresponding line on substrate 180. The line image is arranged along a spatial dimension. The line image passes through diffraction grating 570. Diffraction grating 570 receives the line image and dissects each sub-portion of the line image into its constituent wavelength components, which are arranged along a spectral dimension. In one embodiment, the spectral dimension is perpendicular to the spatial dimension. The result is a two-dimensional spectral line image that is captured by two-dimensional imager 580. In one embodiment, the imager is a CCD, the spatial dimension is the horizontal dimension, and the spectral dimension is the vertical dimension. In this embodiment, the spectral components at each horizontal CCD pixel location along the aperture image are projected along the vertical dimension of the CCD array.

A imaging spectrometer 511, for example, is available from Filmetrics, Inc. of San Diego, Calif. In this spectrometer, transmission diffraction grating 570 is available from Optometrics of Ayer, Mass. (e.g., Part No. 34-1211). Two-dimensional imager 580 is a CCD imager incorporating a Model Turan line scan camera manufactured by Dalsa Inc., with 2048 pixels in the system spatial direction, and 96 pixels in the system spectral direction. Two-dimensional imager 580 is operated in area scan mode, with only the first 32 rows of pixels read out. Two-dimensional imager 580 is further configured to operate in an analog mode to generate the video signal. This results in a data read rate greater than 1000 frames per second. Thirty-two rows of spectral data are sufficient for measurement of thicknesses in the range required for layers polished by CMP tools.

If used with a single wavelength light source, two-dimensional imager 580 can be replaced with a one-dimensional imager. Though a one-dimensional imager is adequate for some applications where an especially low-cost whole-wafer imaging system is required, the loss of spectral information can lead to less precise and more ambiguous measurements of the film thickness and other wafer characteristics.

The numerical aperture of the lens 560 is approximately 0.06, which is considerably smaller than that of sensor fiber 320. By minimizing bends in sensor fiber 320 during assembly, the light propagating through sensor bundle 172 undergoes only minimal mixing, so that the detector senses light from a smaller cone angle than the numerical aperture of 0.22 of the sensor fibers 320 would indicate. Thus, lens 560 can be selected to have a NA that sets the effective spot size of the individual sensor fibers.

With reference to FIG. 1 and FIG. 4A, sensor fibers 320 at the sensing end of sensor bundle 172 are arranged in a sequence (e.g. left to right) that matches the sequence of fibers at the other end of sensor bundle 172 (e.g., the end coupled to optoelectronics assembly 115). This arrangement preserves the orientation of data points and facilitates data processing. However, such a pre-determined sequence is not necessary to the embodiments described herein. The sequence of sensor fibers 320 can be arbitrary and unknown to facilitate fabrication of fiber assembly 125 and sensor bundle 172. To determine the actual sequence of fibers 320, light shined through each individual sensor fiber 320 is detected on two-dimensional imager 580, thereby creating a map of input light to detected light. Once measured, this map is saved, and all subsequent measurements sorted out using this map. Data point spacing provided by the spatial field of the sensor fibers can thus be properly reconstructed by system controller 108 during the imaging process, regardless of sensor fiber sequence at either end.

FIGS. 6A through 6E provide a method of fabricating fiber assembly 125. Fiber assembly 125 further includes plate 610 and plate 630, both of which have a thickness approximately equal to half the radius of illumination fibers 310 so that together they have a thickness slightly greater than the radius of illumination fibers 310. Plate 610 is patterned with parallel grooves 620 to a depth of approximately the radius of sensor fibers 320, as shown in FIG. 6A. Plate 610 and plate 630 are made of metal such as aluminum or stainless steel but are not so limited. Electropolishing is used to form grooves 620. Plate 610 and plate 630 can also be made of other materials, e.g. silicon (with grooves 620 formed using lithographic techniques and etching).

Once grooves 620 have been formed, sensor fibers 320 are positioned therein. Sensor fibers 320 are then secured in place using an epoxy-based adhesive (epoxy not shown). Referring to FIG. 6B, plate 630 is then positioned on top of sensor fibers 320 in grooves 620 of plate 610 and glued in place with epoxy. Illumination fibers 310 are then positioned on the surface of plate 630 opposing grooves 620, as shown in FIG. 6C, and secured in place using epoxy. Then, illumination fibers 330 are positioned on the surface of plate 610 opposing grooves 620, and secured in place using epoxy. This portion of the assembly process results in an end-view configuration as shown in FIG. 6C, and in side view as shown in FIG. 6D. The fibers are then cleaved and polished so that fiber ends 192 a, 194 a and 194 b are co-planar, as shown in FIG. 6E. Illumination fibers 310 and illumination fibers 330 are then bundled to form illuminator bundle 174 using methods known in the art. Likewise, sensor fibers 320 are bundled to form sensor bundle 172.

FIGS. 7A through 7C provide an alternate method of fabricating fiber assembly 125. Plate 610′ and plate 630′ are similar to plate 610 and plate 630 respectively, except that no grooves are formed. To obtain sensor fibers 320, sensor fibers 620 are positioned on plate 610′, as shown in FIG. 7A, and secured in place using epoxy (not shown). Plate 630′ is positioned against sensor fibers 620 and secured in place using epoxy (not shown), as shown in FIG. 7B. The rest of the assembly is similar to that shown in FIG. 6. Once assembled, periodic sensor fibers, e.g. every sixth fiber, is selected to form sensor fibers 320, as shown in FIG. 7C.

FIG. 8 is a flow diagram for collecting and analyzing 800 reflectance data from the surface of substrate 180, under an embodiment. The collecting and analyzing 800 includes collecting a series of line images using spectrometer 190 as fiber assembly 125 sweeps under carrier 170 and substrate 180. The sequence of line scans resulting from fiber assembly 125 sweeping under substrate 180 constitutes a frame. Each rotation of platen 135 causes fiber assembly 125 to sweep under substrate 180 and produce additional frames. The sequence of frames, once suitably analyzed, provides a wealth of information about the polish process. For example, a single frame, or a combination of frames, may be used to construct a two-dimensional image of substrate 180.

The CMP system controller provides the rotation rate of platen 135, the rotation rate of carrier 170, and the angle reference signal. The angle reference signal constitutes a trigger signal, which, along with knowledge of the platen rotation rate, allows the imaging system 105 to initiate data collection just as fiber assembly 125 begins to pass beneath the leading edge of retaining ring 182 and to pause data collection just as fiber assembly 125 completes its sweep beneath substrate 180 and the trailing edge of retaining ring 182. Thus, the position of the substrate 180 is known; however the rotational position of substrate 180 on carrier 170 is not known.

Each series of line images includes spectral reflectance of the light from each sensor fiber 320. Since the position of each sensor fiber under the carrier 170 is known (relative to platen 135, not with respect to any particular rotational position of carrier 170), a line image therefore comprises a set of reflectance measurements versus position along a curve that is approximately a chord across substrate 180. By collecting a sequence of line scans as fiber assembly 125 sweeps under substrate 180, spectral reflectance data for an entire wafer can be obtained in a single pass of fiber assembly 125 under substrate 180. The collecting and analyzing 800 provides a way of collecting this spectral data in each frame, and re-mapping the spatial information to form an image of substrate 180 as a function of time. The image may thus comprise a two-dimensional image, having both a spatial dimension and a spectral dimension.

The spectrometer readout rate determines the sampling frequency. The platen rotation rate determines the amount of time fiber assembly 125 is under substrate 180, which when combined with the sampling frequency allows a user to select a suitable data density and hence image resolution. After collecting a set of line images collected during a single sweep, the data is corrected for the rotation of substrate 180 relative to platen 120. The result is an image, which can be analyzed to yield significant process information. The data, either raw or processed, can also be stored to allow the imaging system 105 to generate time dependent images of substrate 180 during CMP. These images can also be analyzed to produce a wealth of valuable process information.

Initializing the imaging system 105 involves obtaining initialization data from the CMP tool to set the basic operating parameters of the imaging system 105. The initialization data includes the nominal carrier rotation rate, the platen rotation rate, R_(OFFSET) (and any programmed changes in R_(OFFSET)), and the angle reference signal. Controller 195 uses the angle reference signal to generate a start data acquisition signal so that data is collected only while fiber assembly 125 is beneath carrier 170.

In operation, the imaging system 105 acquires 810 a sequence of line scans as fiber assembly 125 sweeps under carrier 170 holding substrate 180. Each line scan comprises a set of reflectance data from each of the sensor fibers 320 that make up sensor bundle 172. The sequence of line scans corresponding to a single sweep of fiber assembly 125 under carrier 170 forms a frame. FIGS. 9A through 9C show this process, and in particular show fiber assembly 125 in each of three positions as it sweeps under substrate 180. FIGS. 9A through 9C show a trajectory 910 of a sensor fiber 990, under an embodiment.

The acquisition 810 includes sensing how much light is being received by integrating light received by spectrometer 190, for example by determining whether the light falls between an acceptable minimum (meaning that there is sufficient light to make measurements) and a maximum (above which there is signal saturation). Then, if need be, the intensity of the light can be adjusted to provide a better signal to noise ratio. The intensity can be adjusted by changing the integration time or by changing the light intensity. Then, by knowing the platen rotation rate and the carrier rotation rate, a transit time can be calculated. This transit time corresponds to the time taken by fiber assembly to sweep under retaining ring 182 and substrate 180. The transit time can also be determined empirically.

One such way to determine the transit time empirically is to examine the reflectance measurements of sensor 990 as it follows trajectory 910. Since the reflectance measurements from retaining ring 182 differ from those of substrate 180, the actual time to traverse trajectory 910 beneath substrate 180 and retaining ring 182 can be determined. Whether using a calculated transit time or an empirically determined transit time, the transit time is then divided by a measurement sampling rate to deduce a number of line scans per frame, and thus the data density.

The collecting and analyzing 800 further includes determining 820 which frame includes the center point of substrate 180 in order to enable the substrate image to be properly oriented. This allows the imaging system 105 to monitor specific sites on a wafer. Again referring to FIGS. 9A through 9C, each frame includes a line image extending across substrate 180. For simplicity, FIGS. 9A through 9C show fiber assembly 125 to include fewer sensors than the number that might typically be included in the fiber assembly 125 (e.g., only twelve sensors are shown but the imaging system 105 can include any number of sensors).

Each line image includes a signature portion corresponding to the reflectance of retaining ring 182. As fiber assembly 125 sweeps under carrier 170, reflected light collected by sensor bundle 172 includes at first only light reflected from retaining ring 182, which indicates the edge of carrier 170. Once fiber assembly 125 is positioned under substrate 180, one or more sensor fibers collect reflected light from substrate 180 as well as signature light from retaining ring 182. FIG. 9A shows an example of fiber assembly 125 just after it has passed under the leading edge of retaining ring 182 so that some sensor fibers are positioned beneath retaining ring 182 and other sensor fibers are beneath substrate 180. In particular, sensor 940 and sensor 930 collect light from retaining ring 182 while the sensors between them, including sensor 920, collect light reflected from substrate 180. In FIG. 9A there are 7 sensors that collect light from substrate 180.

FIG. 9B shows the position of fiber assembly 125 at a slightly later time than in FIG. 9A. Sensor 960 and sensor 950 collect signature light from retaining ring 182. Ten sensors, including sensor 930, sensor 970, and all of the other sensors between sensor 930 and sensor 970 collect light reflected from substrate 180. FIG. 9C shows the position of fiber sensor 125 at a slightly later time than in FIG. 9B. In FIG. 9C, sensor 930 and sensor 940 collect signature light from retaining ring 182. Seven sensors, including sensor 920, sensor 980, and all of the other sensors between sensor 920 and sensor 980 collect light reflected from substrate 180.

Thus, as fiber assembly 125 sweeps across substrate 180, more and more sensors collect light reflected from substrate 180 up to a maximum, followed by fewer and fewer sensors collecting reflected light until fiber assembly 125 passes under the trailing edge of retaining ring 182. By determining the maximum number of sensors that collect light reflected from substrate 180 in the collection of line scans that comprises a frame, the line scan closest to the center of substrate 180 can be identified. The midpoint of reflectance measurements corresponding to reflectance off substrate 180 and between the signature reflectance measurements of this line scan corresponds to the center of substrate 180. Each frame is labeled with a frame number to allow a time ordering of frames.

The collecting and analyzing 800 further includes uses knowledge of the platen rotational speed and knowledge of the location of the carrier center to predict 830 the wafer center in each frame. The predicting 830 uses coordinate transformations as known in the art.

The collecting and analyzing 800 further includes combining knowledge of the frame number, the carrier rotation speed, and the location of the wafer center to un-rotate 840 the substrate 180. The un-rotation 840 is included in an embodiment because between each line scan substrate 180 rotates and this distorts the image. The un-rotation 840 includes coordinate transforms known in the art. The collecting and analyzing 800 of an embodiment thus yields a round wafer image when substrate 180 is round, as is the case when planarizing semiconductor wafers.

The collecting and analyzing 800 further includes image processing techniques to form 850 a wafer image from the spectral data for each sensed location. The “dark” response is subtracted, the image is scaled to the correct size so that it fits in the display area, and averaging techniques used to smooth roughness in the spectral profiles. One general averaging technique is to use box-car averaging on the spectral data for each pixel of two-dimensional imager 580. For reflectance data from metal surfaces, one specific averaging technique is to average all of the spectral data within a pre-determined wavelength range, and repeat this process for all the sensed locations. In one embodiment, the pre-determined wavelength range is chosen to encompass the entire range of sensitivity of two-dimensional imager 580. In another embodiment, the pre-determined wavelength range is chosen to encompass only a portion of the entire range of sensitivity of two-dimensional imager 580. Such a technique can be used to minimize, or even eliminate, reflectance variations caused by interferometric effects of underlying layers. In yet another embodiment, the pre-determined wavelength range is chosen to encompass only a very small portion of the entire range of sensitivity of two-dimensional imager 580, namely that sensed by a single pixel. This embodiment corresponds to using a single wavelength source of light.

The formation 850 of a wafer image further includes rotating the image to orient the notch (in the case substrate 180 is a semiconductor wafer) to a pre-specified orientation, either notch up, notch down, notch left, or notch right. One way to orient substrates involves detecting the notch in the acquired wafer image. With approximately 300 sensor fibers 320 sweeping across substrate 180 with a typical sampling rate of 1 kHz, features as small as 1 mm can be detected. Since the notch on semiconductor wafers is approximately 2.5 mm by 2 mm, it is readily detected using techniques known in the art. By comparing the expected substrate orientation from frame-to-frame with measured orientation, substrate slippage can be detected and quantified modulo 2π.

The collecting and analyzing 800 further includes analyzing 860 the spectral images to extract additional information. The type of additional information depends in part on the material being polished, i.e., metal or dielectric. The type of additional information also depends on the intended use of the additional information. For example, for endpoint detection applications, it is essential to learn when to terminate a given process (or process step). For process control applications it is important to monitor the performance of a given CMP tool, and to provide corrections to CMP tool process parameters if needed. For polish control applications, it is important to ensure minimal non-uniformity and correct remaining film thickness upon the conclusion of a CMP process, and to know what the non-uniformity and remaining film thickness is at the end of a polish process.

In the case of metal layers being polished, it is very useful to know whether there is any residual metal, and if so where it is. One technique for assessing the presence of residual metal is to compare the average reflectance within a pre-determined spectral range to a threshold value for each sensed location across substrate 180.

FIG. 10 shows an example image 1010 of a partially processed silicon substrate during a CMP process. The substrate used for this example is made of silicon, and has been partially processed to include the deposition of copper film. During the CMP process, the bulk of the copper film must be removed so that residual metal forms desired conductive paths. One essential characteristic of the CMP process is that all residual metal be removed. FIG. 10 shows several regions 1020 that have not cleared. The trajectory of any single sensor across the substrate would not necessarily have traversed any of the uncleared regions. The embodiments described herein scan the entire substrate and therefore make possible a more reliable assessment of the status of the CMP process.

Assessing dielectric film stacks is more complex due to the variation in spectral response as the thickness changes as well as the variety of film stacks that can contribute to any given reflectance measurement. One technique for dealing with dielectric films is to select one particular film stack present on a substrate, and compare measured reflectance with a calculated reflectance for a given top layer thickness by calculating a fitting parameter, for example, using such known techniques as least-squares. By varying the thickness of the top-most layer in the calculated reflectance and looking for a minimum in the least squared fit, the actual thickness can be determined.

Because there are thousands of measurements made over the entire substrate, many options exist. Measurements can be made at specific sites on substrate 180, using site coordination information provided to controller 108 of the imaging system 105 via rotating coupler 110. Such sites can correspond to specific die, or they can correspond to well known measurement maps such as a polar map or Cartesian maps with 49 (or other) sites. Measurements using the embodiments herein can also be used to determine such significant process performance characteristics as non-uniformity. Although such measurements are typically performed only after the completion of a CMP step, the embodiments described herein provide for reporting of non-uniformity in addition to residual film thickness upon the completion of CMP.

An additional analysis step of the embodiments herein allows for the determination of significant process metrics such as remaining film thickness in specific, pre-determined regions on substrate 180, and communicating such metrics to the CMP system controller during a CMP polish process. This capability is particularly important in multi-step CMP processes such as those used to polish copper films. These processes can include different process recipes, including different slurries, depending on the metal film being polished. Thus, the imaging system 105 is used to detect the clearing of one metal, e.g. copper, which exposes a barrier film such as tantalum. For this situation, the imaging system 105 measures the clearing of the copper film, communicates this clearing to the CMP system controller, and continues to monitor the CMP process while the tantalum is polished.

The embodiments described herein can also be used as part of a feedback control system, especially when used with carriers that have one or more pressure zones and the ability to adjust the pressure within a given zone according to need. To implement such a feedback control system, the CMP system controller communicates site location information to the imaging system 105 via rotational coupler 110. The imaging system 105 then measures the substrate 180, identifies sites on substrate 180 that coincide with the site location information, and reports via rotational coupler 110 the metrics for the desired sites. The CMP system controller then adjusts tool parameters such as zonal pressure to improve process performance. This process can be applied while polishing a substrate, or it can be applied in a run-to-run mode by using measurements on one substrate to affect polish parameters on a following substrate.

The collecting and analyzing 800 further includes storing data and determining 870 whether or not the process is complete. If the process is complete, the collecting and analyzing 800 ends. If the CMP process is not complete, the collecting and analyzing 800 returns to collect 810 additional reflectance data.

The systems and methods described herein can be used to image, during CMP processing, portions of a substrate that are less than an entire substrate. The result is a set of data corresponding to one or more swaths across substrate 180. A swath is the portion of substrate 180 being sensed; a data swath is the optical data obtained from the swath. In this embodiment each swath has a width that is at least as large as the die on the substrate. By analyzing such swaths, individual die can be identified and the orientation of substrate 180 can be determined. Furthermore, individual sites within die can be measured and the CMP system controller informed of such measurements.

Streets are non-used portions of substrate 180 between integrated circuits on substrate 180. An integrated circuit surrounded by streets forms a die. Though each die is rectangular in shape, die can also be made in squares. Although planar die have symmetry (two-fold for rectangular die and four-fold for square die), die containing integrated circuits typically do not have symmetry because each die contains functional elements that lead to a non-uniform visual appearance that can be detected.

With reference to FIG. 11, whole die imaging system 105′ includes an aperture 130′ formed in platen 120 so that the length of aperture 130′ is less than the diameter of substrate 180. A fiber assembly 125′ disposed within aperture 130′ is arranged along a radial line extending from rotational coupler 110. Polish pad 135 has a window 137′ that is smaller than substrate 180, and that serves to allow light to be emitted from fiber assembly 125′ and subsequently received by fiber assembly 125′ upon reflection from substrate 180. The other elements in FIG. 11 are otherwise similar to those in FIG. 1. FIG. 12A shows the nominal position of fiber assembly 125′ in aperture 130′, and arranged so that in normal operation, fiber assembly 125′ passes under or nearly under the center of substrate 180. FIG. 12B is otherwise similar to FIG. 2B.

Fabrication of fiber assembly 125′ is identical to that of fiber assembly 125 except that the overall length of fiber assembly 125′ is chosen to be approximately as large as, or slightly larger than, the size of the die on substrate 180. In one embodiment, fiber assembly 125′ has a length of 20 mm, corresponding to approximately 27 sensor fibers if the sensor fibers are located on centers of approximately 0.73 mm. Imaging system 105′ produces two-dimensional arrays of 10×10 to 20×20 data points, depending on die size.

FIG. 13 shows an example of fiber assembly 125′ sweeping along a trajectory 1310 that passes under retaining ring 182 and substrate 180 to form swath 1320. Swath 1320 further includes a transverse dimension 1325 that is approximately equal to the length of fiber assembly 125′. Substrate 180 further includes many complete die 1330 and may also include partial die 1340.

Die 1330 include partially processed integrated circuits and un-used portions of substrate 180 that surround the partially processed integrated circuits. Numerous streets 1350 and transverse streets 1355 separate adjacent integrated circuits.

Partial die 1340 are portions of partially processed integrated circuits that serve to facilitate the fabrication of adjacent die, but are otherwise non-functional.

In operation and with continuing reference to FIG. 11, substrate 180 loaded into carrier assembly 170 is pressed into polish pad 135 while carrier assembly 170 rotates about axis of rotation 155, platen 120 rotates about axis of rotation 150, and slurry flows across polish pad 135. A combination of chemical and mechanical processes abrades material from the surface of substrate 180, i.e., from die 1330 and partial die 1340. While the polishing process takes place, optoelectronic assembly 115 generates light based on the power and control signal generated by the variable power supply generator within system controller 108. This light passes through optical illuminator bundle 174 to fiber assembly 125′, where it illuminates wafer 180 as aperture 130′ passes under wafer 180. Fiber assembly 125′ also receives light reflected from wafer 180, and directs this reflected light into sensor bundle 172. Optoelectronic assembly 115 receives the reflected light and converts it into the video signal than can be converted into an image of a portion of substrate 180 by system controller 108.

FIG. 14 is a flow diagram for collecting and analyzing 1400 reflectance data from the surface of substrate 180, under an embodiment. Collection and analysis 1400 of data is similar to collection and analysis 800 as described above with reference to FIG. 8 with the exception that determining substrate orientation by identifying the location of the notch is replaced (e.g., forming 1450 wafer image) since an arbitrary swath does not necessarily include the notch.

The collecting and analyzing 1400 includes image processing techniques to clean up the spectral data for each sensed location. The “dark” response is subtracted, the image is scaled to the correct size so that it fits in the display area, and averaging techniques used to smooth roughness in the spectral profiles. One general averaging technique is to use box-car averaging on the spectral data for each pixel of two-dimensional imager 580. For reflectance data from metal surfaces, one specific averaging technique is to average all of the spectral data within a pre-determined wavelength range, and repeat this process for all the sensed locations. In one embodiment, the pre-determined wavelength range is chosen to encompass the entire range of sensitivity of two-dimensional imager 580. In another embodiment, the pre-determined wavelength range is chosen to encompass only a portion of the entire range of sensitivity of two-dimensional imager 580. Such a technique can be used to minimize, or even eliminate, reflectance variations caused by interferometric effects of underlying layers. In yet another embodiment, the pre-determined wavelength range is chosen to encompass only a very small portion of the entire range of sensitivity of two-dimensional imager 580, namely that sensed by a single pixel. This embodiment corresponds to using a single wavelength source of light.

Since the location of the notch is not known, wafer orientation is determined using swath data. Edge detection techniques are used to orient the substrate modulo π/2, as shown in FIG. 15A. Note that actually presenting an image of swath 1320, as shown in FIG. 15A is not necessary, but the orientation of streets 1350 and transverse streets 1355 within the swath data are determined.

To determine the orientation of substrate 180, a die 1360 in swath 1320 is examined for optical non-homogeneities. Since integrated circuits are not homogeneous, the light reflected from them is also non-homogeneous. Thus, light reflected from some portions of die 1360 have differences compared to other portions of die 1360. One example of a difference is a color difference due to one portion having more metallization lines or being composed of materials having different optical properties and thicknesses. A second difference is an intensity difference due for example to more metal in one portion than other portions. Such differences in intensity can also be due to different absorption occurring within one portion of die 1360 compared to a different portion. A third difference arises by combining the first two differences, i.e., examining the intensity of light in a narrow wavelength region corresponding for example to a null region where light interferes destructively, thus giving a dark appearance. The choice of wavelength for examining reflected light depends on the optical properties of the film stack being examined, and this wavelength can be varied during the polish process. When polishing metal layers where the reflectance is nearly uniform until the metal layer is only a few hundred nanometers thick, intensity variations are used.

One way to examine the light reflected within die 1360 is to partition the light from die 1360 into quadrants, as shown in FIG. 15B, and to compare the intensity of light within each quadrant. So long as one quadrant is either brighter or dimmer than the other quadrants, as represented by a spot 1380, the orientation of substrate 180 is determined uniquely.

One way to enhance the reliability of detecting substrate orientation is to examine more than one die. Examining more than one die also provides information about the polishing uniformity of the CMP process.

Depending on the length of fiber assembly 125′ and the dimensions of die 1360 (which may differ as manufacturing needs change), swath 1320 may not necessarily include an entire die. In this case streets are detected and a comparison made that includes the light reflected from quadrants surrounding an intersection 1370 of a street and a transverse street, as indicated by a spot 1382 in FIG. 15C. Since the die-to-die reflectance pattern is nominally the same, substrate orientation is determined uniquely once spot 1382 is located. With this technique it is not necessary that the length of fiber assembly 125′ exceed the length of die 1360, i.e., it is not necessary that an entire die 1360 be imaged to determine the orientation of substrate 180, which significantly enhances the flexibility of the embodiments herein. This technique thus uses sufficient sensor fibers 320 in fiber assembly 125′ in order to identify intersection 1370, and assumes the portions of die surrounding intersection 1370 are large enough that optical reflectance differences can be detected.

Fiber assembly 125′ can be formed in more than one section to allow two or more swaths across substrate 180 to be sensed. If fiber assembly 125′ is formed in more than one section that each section can be disposed within platen 120 at different angles to allow carrier 170 to partially rotate substrate 180 between measurements, thus ensuring that sequential swaths within a single platen revolution are approximately perpendicular to each other (or at another angle with respect to each other if desired). In this embodiment, additional windows 137′ in polish pad 135 may be included. Since carrier rotation rates are often nearly the same as platen rotation rates, displacing a first portion of fiber assembly 125′ from a second portion of fiber assembly 125′ by 90 degrees yields nearly perpendicular swaths.

If the length of transverse dimension 1325 is sufficiently small then fiber assembly 125′ can be modified by replacing sensor bundle 172 with an optical assembly 1640 that couples light reflected from the surface of substrate 180 directly to line imaging spectrometer 1611.

FIG. 16A shows a line imaging spectrometer 1611 that is similar to line imaging spectrometer 511 except that sensor bundle 172 is replaced with lens assembly 1640 and aperture 1650. Line imaging spectrometer 1611 further comprises a lens assembly 560, a diffraction grating 570, and a two-dimensional imager 580. Line imaging spectrometer 1611 operates as follows. Light from source 160 passes through illumination bundle 174, and impinges on a film contained on or in substrate 180. The light reflects from the wafer and is passed through the platen aperture (not shown) and received by lens assembly 1640. Lens assembly 1640 couples the light through aperture 1650 to produce a line image of a corresponding line on substrate 180. In one alternative embodiment, aperture 1650 may be placed in close proximity to substrate 180, and lens assembly 1640 may be omitted, as shown in FIG. 16B. In another alternative embodiment, lens assembly 560 may be placed in close proximity to substrate 180, and lens assembly 1640 and aperture 1650 may be omitted, as shown in FIG. 16C. The line image is coupled to lens assembly 560 and arranged along a spatial dimension. The line image passes through diffraction grating 570. Diffraction grating 570 receives the line image and dissects each subportion of the line image into its constituent wavelength components, which are arranged along a spectral dimension. In one embodiment, the spectral dimension is perpendicular to the spatial dimension. The result is a two-dimensional spectral line image that is captured by two-dimensional imager 580. In one embodiment, the imager is a CCD, the spatial dimension is the horizontal dimension, and the spectral dimension is the vertical dimension. In this embodiment, the spectral components at each horizontal CCD pixel location along the aperture image are projected along the vertical dimension of the CCD array.

Since the embodiments described herein provide for many reflectance measurements within a die, selected sites within the die can be monitored during the CMP process, thus providing valuable information about changes in the surface of substrate 180 as it is being polished. The embodiments described herein can monitor film thickness (when polishing dielectric materials), within-substrate uniformity, die-to-die uniformity, and dishing. All of this process information is communicated to CMP system controller via system controller 108.

Orbital CMP machines are another type of planarization tool for which process information, including endpoint detection, is useful. Orbital tools provide relative motion between a polish pad and a substrate by rotating one and orbiting the other. Numerous examples of orbital motion have been disclosed. U.S. Pat. No. 5,554,064 for example discloses an approach that involves rotating the substrate and orbiting the polish pad. In addition, U.S. Pat. Nos. 5,582,534 and 5,938,884 disclose other mechanisms for creating an orbital motion for polishing a substrate.

The use of orbital motion typically involves the polish pad undergoing small-radius orbital motion about a center point aligned with the rotational axis of the substrate. An orbital radius of approximately 16 mm (⅝ inch) leads to small radius orbital motion. Thus, each point on the polish pad that is in contact with the substrate follows a trajectory constrained to an annular portion of the substrate. In contrast to other planarization tool designs the substrate is exposed to a relatively small portion of the total polish pad area, i.e., the polish pads are only slightly larger than the substrate. The substrate is held by a carrier that is used to press the substrate into the polish pad in the presence of slurry that is delivered to the pad via holes in the pad. Pressure applied to the substrate varies temporally according to polish recipes. Recently developed CMP carrier designs include techniques for varying the pressure spatially across the wafer during polish processes to improve planarization uniformity.

Numerous optical endpoint detection approaches for orbital CMP have been disclosed including U.S. Pat. No. 6,805,613 and patents cited therein. These patents involve sensing reflected light on a point-by-point basis. Most involve detecting light over a broad range of wavelengths, and inferring any of various process conditions from an analysis of the reflected light. Collectively, however, conventional optical endpoint detection for orbital CMP suffers from some limiting problems.

Conventional optical endpoint detection for orbital CMP involves slow data acquisition, which implies sparse data density for measurements made during a normal CMP process cycle time. These approaches basically involve sweeping light across a substrate during CMP and sensing the reflected light, these approaches are intrinsically serial. Consequently, these approaches constrain the rate at which data can be collected. In addition, collecting more data requires additional hardware, which increases cost. Some of these systems disclose the use of multiple sensors to acquire more data. However, the approach remains serial in nature, which limits the amount of data that can be collected and analyzed while the substrate is being polished. What is needed is a cost-effective approach to acquiring large amounts of data during orbital CMP processes.

Conventional optical endpoint detection for orbital CMP also does not allow measurements to be obtained at pre-determined locations on the substrate during orbital CMP. Process control in manufacturing integrated circuits depends on knowing film properties, such as thickness, at specific locations on each substrate. The existing art does not allow acquisition of data at only these locations, nor does it provide a way to acquire sufficient data to ensure that measurements are made at these locations. Consequently, these approaches are very much hit-or-miss, which significantly reduces control. What is needed is a way to provide real-time film thickness measurements at specific pre-determined sites on a substrate during orbital CMP.

The imaging system 1805 of an embodiment allows substrate 180 to be monitored during orbital chemical-mechanical planarization processes. FIG. 17 shows imaging system 1805 that includes a pad structure 1820 with an aperture 1830, a fiber assembly 1825 disposed within aperture 1830, and optoelectronic assembly 115 that is optically coupled to fiber assembly 1825 via illuminator bundle 1874 and sensor bundle 1872.

Imaging system 1805 further includes an electrical connector 1876 that electrically couples optoelectronic assembly 115 to fiber assembly 1825, and an electrical connector 1877 that electrically connects optoelectronic assembly 115 to a system controller 1808. Optoelectronic assembly 115 can be attached to pad structure 1820 to minimize connector lengths, or it can be located remotely from pad structure 1820 to minimize the risk of vibrations damaging the unit. System controller 1808 and electrical connector 1877 are located remotely from pad structure 1820.

Imaging system 1805 is used in a CMP tool 1800 that further includes a polish pad 1835 mounted on pad structure 1820, a motor (not shown) that causes pad structure 1820 to orbit about axis of rotation 1850 at an orbit rate, a carrier assembly 1870 rotated by a second motor (also not shown) about axis of rotation 1850 at a carrier rotation rate. Carrier assembly 1870 includes a retaining ring 1882 that secures substrate 180 in place during the polish process. A slurry delivery system (not shown) delivers slurry through multiple holes in polish pad 1835 so that orbital motion disperses the slurry over polish pad 1835. A CMP system controller (not shown) controls the operation of the CMP tool, and is operationally connected to system controller 1808.

Fiber assembly 1825 is similar to fiber assembly 125 described above except it is configured to be thinner to accommodate the limited space available in pad structure 1820. Fiber assembly 1825 is oriented along a radial line extending away from the center of polish pad 1835 on pad structure 1820, as shown in FIG. 18. In particular, fiber assembly 1825 includes several hundred sensing fibers, each of which senses light from a small (e.g., approximately 1 mm) spot on substrate 180 during each measurement.

Referring again to FIG. 17, pad structure 1820 is a multipurpose element that provides a working face 1822 to which polish pad 1835 is adhered, a slurry distribution header assembly (not shown), and a functional platform from which optical reflectance measurements can be made. Working face 1822 has a radius that is larger than the diameter of substrate 180 plus the orbital radius. Working face 1822 is a solid disk except for portions the disk that have been removed to form the functional platform for fiber assembly 1825, illuminator bundle 1874, and sensor bundle 1872 of imaging system 1805. However, as described above it is not necessary that the disk be solid to practice the embodiments described herein, and other arrangements such as a hollow disk or a thin, solid disk over a honeycomb core can also be used. Additionally, aperture 1830, which is shown throughout the figures as being cut into pad structure 1820 in a generally rectangular form, is not restricted to a rectangular form as described above. Aperture 1830 comprises an opening in working face 1822, which opening may comprise any shape through which light may pass for the purposes of capturing reflectance data from a substrate 180. Accordingly, aperture 1830 may be rectangular, circular, oblong, symmetrical, asymmetrical, or any other shape.

Electrical connector 1876 and electrical connector 1877 are identical to electrical connector 176 and electrical connector 177 in terms of function, and differ due to engineering modifications to accommodate differences between rotational CMP tools and orbital CMP tools. They deliver synchronization and control signals, as well as power, to optoelectronic assembly 1815.

Polish pad 1835 (e.g., an IC1000 from Rodel Corporation) includes an optical element (or window) 137 that transmits light, and attaches adhesively to working face 1822 of pad structure 1820. Polish pad 1835 also has a number of holes through which slurry is delivered. Window 1837 is transparent in one embodiment (e.g., formed from JR111 material from Rodel Corporation), but in another embodiment polish pad 1835 is instead transparent.

Optoelectronic assembly 1815 is similar to optoelectronic assembly 115, except it is optically coupled to fiber assembly 1825 via illuminator bundle 1874, and sensor bundle 1872. Functionally, optoelectronic assembly 1815 is similar to optoelectronic assembly 115. Optoelectronic assembly 1815 is electrically connected to fiber assembly 1825 via Electrical connector 1876 and electrical connector 1877. Optoelectronic assembly 1815 generates light that propagates into illuminator bundle 1874, and receives light from sensor bundle 1872, which optoelectronic assembly 1815 converts to an electrical signal. The electrical signal is directed to system controller 1808 via electrical connector 1876 for use by the system computer. This electrical signal can be structured to represent the image of substrate 180, or it can be structured to signal the CMP system controller to stop polishing or to go to the next polish step.

Illuminator bundle 1874 and sensor bundle 1872 are identical to illuminator bundle 174, and sensor bundle 172, except for mechanical modifications to accommodate use in CMP tool 1800.

System controller 1808 is similar to system controller 108 except for modifications to accommodate use in CMP tool 1800.

In operation, substrate 180 is loaded into carrier assembly 1870 and then pressed into polish pad 1835 while carrier assembly 1870 rotates substrate 180 about axis of rotation 1850, pad structure 1820 orbits about axis of rotation 1850, and slurry flows through polish pad 1835. A combination of chemical and mechanical processes abrades material from the surface of substrate 180. While the polishing process takes place, optoelectronic assembly 1815 generates light based on the power and control signal generated by the variable power supply generator within system controller 1808. This light passes through optical illuminator bundle 1874 to fiber assembly 1825, where it illuminates wafer 180 through aperture 1830, which is under wafer 180. Fiber assembly 1825 also receives light reflected from wafer 180, and directs this reflected light into sensor bundle 1872. Optoelectronic assembly 1815 receives the reflected light and converts it into the video signal than can be converted into an image of substrate 180 by system controller 1808.

FIG. 18A shows a top view of the pad structure, and in particular shows fiber assembly 1825 viewable through polish pad 1835. FIG. 18B shows an example trajectory of a single point of polish pad on substrate 180 during orbital motion, and in particular shows how the trajectory is constrained to an annular region having an inner radius of R1 and an outer radius of R2. If fiber assembly 1825 is disposed away from the center of polish pad 1835, the trajectory of any sensor fiber is constrained to an annular region. Note, however, that if fiber assembly 1825 is in close proximity to the center of polish pad 1835, then the inner radius R1 shrinks to 0 and the region assumes a disc shape.

The carrier rotation rate is less than the orbital rotation rate, and a ratio of orbital rotation rate to carrier rotation rate of approximately 16 is suitable. (The orbital rotation rate is approximately 600 orbits per minute.) The embodiment is not limited however to ratios of approximately 16. The exact ratio of an embodiment differs from an integer by a small amount. If the ratio is integral, then the trajectory overlaps itself, which can cause the reproduction of polish pad imperfections on the polished substrate. From an imaging perspective, an integral ratio means that only a portion of the annular region is imaged. By changing the ratio from an integral value by a small amount, the trajectory tends to fill the annular region; likewise, the entire annular region can be imaged.

FIG. 19 shows an image 2080 of substrate 180 showing an outer annular region 2010 that is devoid of measurement data, an inner disc 2020 that is likewise devoid of data, and an annular region 2030 of reflectance measurements. Note that annular region 2030 has an inner radius of R3 and an outer radius of R4. Since fiber assembly 1825 is oriented along a radial line extending away from the center of polish pad 1835 on pad structure 1820, R4 corresponds to sensor fibers located farther away from the center of polish pad 1835. Likewise, R3 corresponds to sensor fibers located nearer to the center of polish pad 1835. Thus, the annular region 2030 has a width (R4-R3) that exceeds the radial width (R2-R1) of an individual point.

In operation, the orbital motion of pad structure 1820 causes each sensor fiber of fiber assembly 1825 to follow a trajectory like trajectory 1920. However, since there are hundreds of sensor fibers in a fixed orientation, viz., extending along a radial line from the center of polish pad 1835, large swaths of measurements are obtained. System controller 1808 records all this data, along with positional information of pad structure 1820 and of carrier 1870, which allows each measurement to be associated with a specific coordinate (e.g., x coordinate and y coordinate) on substrate 180. System controller 1808 then compiles the reflectance and spatial locations of the measurements to generate image 2080. Partially or fully overlapping data points are overwritten by the more recent measurements, which reduces data file size. System controller 1808 then analyzes image 2080 using known pattern recognition methods to determine one or more film layer properties at pre-determined locations in annular region 2030. Example locations include bond pads. Having obtained such measurements, system controller 1808 can adjust the process recipe, e.g. by altering the applied pressure (spatially or globally) or other process conditions, by terminating the polish process, etc.

Depending on the spacing of the image sensors in fiber assembly 1825 and on the number of image sensors, reflectance data can include measurements from a substantial portion of substrate 180. If desired, two or more fiber assemblies can be used to obtain either two or more annuli of measurement data (or a larger single annulus comprising multiple, radially contiguous annuli) that maximize the area of annular region 2030.

Use of the line imaging spectrometer of an embodiment allows numerous data points to be acquired simultaneously, i.e. hundreds to thousands of points are collected during each data acquisition cycle, thus providing a hundred- to thousand-fold increase in the number of data points obtained per unit time. The embodiments described herein are also used to form an image of the substrate so that pattern recognition techniques can be used to determine film properties at pre-determined sites on the substrate.

The combination of using the line imaging spectrometer to form images and the use of pattern recognition techniques to analyze the images provides significant benefits in terms of dramatically increased quantity and quality of data, both aspects of which are obtained in situ without adversely affecting CMP performance.

According to an aspect of this disclosure, an imaging system is described. In this system, a carrier holds a substrate, with the substrate having a pad-contacting surface with a maximum planar dimension. A rotating platen has a radius and holds a polishing pad, with the platen including a aperture having a length substantially disposed along its radius and equal to or exceeding the maximum planar dimension of the substrate. The platen includes an optically transparent element located at about the aperture. A frame operatively disposes the rotating platen relative to the carrier, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the aperture within a rotation of the platen. An image processing subsystem captures, from light reflected from the pad-contacting surface and transmitted through the optically transparent element, a plurality of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the substrate during traversal of the pad-contacting surface past the aperture. It then derives therefrom a two-dimensional image, or frame, comprising frame data providing information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

According to another aspect of this disclosure, a method of imaging a substrate is described. In this method, a substrate is held, the substrate having a pad-contacting surface with a maximum planar dimension. In addition, a polishing pad is held by a rotating platen having a radius and including a aperture having a length substantially disposed along the radius and equal to or exceeding the maximum planar dimension of the substrate. The platen includes an optically transparent element located at about the aperture. The rotating platen is operatively disposed relative to the pad-contacting surface, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the aperture within a rotation of the platen. A plurality of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the substrate is captured from light reflected from the pad-contacting surface and transmitted through the optically transparent element during traversal of the pad-contacting surface past the aperture. A frame is derived from the plurality of one-dimensional images. The frame comprises frame data providing information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

According to yet another aspect of this disclosure, a method of forming a fiber assembly is disclosed. In this method, an inner surface of a first plate is patterned with substantially parallel grooves, with the first plate having an outer surface. Individual sensory optical fibers are placed in separate ones of the grooves and secured. An inner surface of a second plate is positioned over the sensory fibers as positioned in the grooves of the first plate, with the second plate having an outer surface. The inner surfaces of the first and second plates are secured together. Illumination optical fibers are positioned on the outer surface of the first plate substantially in parallel with the sensory fibers and secured. Similarly, illumination optical fibers are positioned on the outer surface of the second plate substantially in a parallel with the sensory fibers and secured. The ends of the sensory and illumination fibers are then processed to be substantially co-planar with one another.

According to still another aspect of this disclosure, a method of forming a fiber assembly is disclosed. In this method, sensory optical fibers are positioned substantially in parallel with one another on an inner surface of a first plate, with the first plate having an outer surface. The sensory fibers as positioned on the inner surface of the first plate are then secured. An inner surface of a second plate is positioned over the sensory fibers as positioned on the inner surface of the first plate, with the second plate having an outer surface. The inner surfaces of the first and second plates are secured together. Illumination optical fibers are positioned on the outer surface of the first plate substantially in parallel with the sensory fibers and secured. Similarly, illumination optical fibers are positioned on the outer surface of the second plate substantially in a parallel with the sensory fibers and secured. The ends of the sensory and illumination fibers are then processed so that the same are substantially co-planar with one another.

According to other aspects of this disclosure, an optical fiber assembly is disclosed. The assembly includes a fiber assembly element. A first bundle of illumination fibers is also included. The illumination fibers each have ends which substantially terminate at the fiber assembly element and which are arranged in at least one first and at least one second rows. A second bundle of sensory fibers is also included. The sensory fibers have ends which substantially terminate at the fiber assembly element and which are arranged in a third row between the first and second rows.

Aspects of this disclosure also include an optical fiber assembly. The assembly includes a fiber assembly element. A first bundle of illumination fibers is also included. The illumination fibers each have ends which substantially terminate at the fiber assembly element and which are arranged in first and second rows. A second bundle of sensory fibers is also included. The sensory fibers have ends which substantially terminate at the fiber assembly element and which are arranged in a third row between the first and second rows.

According to further aspects of this disclosure, a die imaging system is described. In this system, a carrier holds a substrate, with the substrate having a pad-contacting surface with a maximum planar dimension and, on one side of the substrate, partially processed integrated circuits separated by streets. A partially processed integrated circuit together with surrounding streets forms a die. A rotating platen has a radius and holds a polishing pad, with the platen including a aperture having a length substantially disposed along its radius and approximately equal to the maximum planar dimension of the die. The platen includes an optically transparent element located at about the aperture. A frame operatively disposes the rotating platen relative to the carrier, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the aperture within a rotation of the platen. An image processing subsystem captures, from light reflected from the pad-contacting surface and transmitted through the optically transparent element, a plurality of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the substrate during traversal of the pad-contacting surface past the aperture. It then derives therefrom a frame comprising frame data providing information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

The embodiments described herein compensate for the wavelength dispersive effects of diffraction occurring at feature edges on integrated circuits. The embodiments described herein also allow measurement site sizes to be smaller than those defined by the geometry and numerical aperture of the sensing fiber. The embodiments also provide for spectral analysis methods based on broadband or narrow band light, and allow measurements to be made for a variable polish pad thickness.

The ability of the embodiments herein to allow measurements of thin-film stacks across an entire substrate provides an image of the entire substrate, and also allow for measurements to be made over multiple film stacks across an entire substrate. The embodiments provide measurements of metal clearing and non-uniformity measurements across an entire substrate throughout metal CMP processes. Furthermore, the embodiments provide residual film thickness and non-uniformity measurements across an entire substrate during and at the conclusion of dielectric CMP.

The embodiments described herein also provide one or more of the following: residual film thickness and non-uniformity measurements in selected regions across a substrate during and at the conclusion of dielectric CMP; substrate measurements suitable for feedback to a CMP carrier with one or more pressure zones; substrate measurements suitable for feedback to a CMP run-to-run control system; methods to obtain images of portions of a substrate being polished; and methods to obtain images of whole and/or partial die on portions of a substrate being polished.

The substrate imaging of an embodiment includes a system comprising a carrier configured to receive a substrate. The system also includes a platen that includes an aperture configured to pass light. The platen is also configured to receive a polishing pad. The system further includes a frame that disposes the platen in a number of positions relative to the carrier. The system also includes an optoelectronic system coupled to the aperture, wherein the aperture passes light of the optoelectronic system to illuminate the substrate and passes reflected light from the substrate to the optoelectronic system. The system also may include a processing system that uses the reflected light to image the substrate as the polishing pad is polishing the substrate.

The polishing pad of an embodiment includes an optical element that is positioned relative to the aperture to pass light to and from the aperture, wherein the optical element is optically transparent.

The optoelectronic system of an embodiment includes an illumination source coupled to the aperture.

The system of an embodiment includes a first set of optical fibers coupled to the illumination source and the aperture.

The optoelectronic system of an embodiment includes an optical receiver coupled to the aperture, the optical receiver configured to receive the reflected light.

The optical receiver of an embodiment is a second set of optical fibers.

The optical receiver of an embodiment includes one or more of a receiver lens assembly and a receiver aperture.

The optical receiver of an embodiment includes a receiver aperture.

The system of an embodiment includes a spectrometer lens assembly configured to receive light from the optical receiver.

The system of an embodiment includes a wavelength-dispersive element configured to receive light from the spectrometer lens assembly.

The system of an embodiment includes an imager configured to receive light from the wavelength dispersive element. The imager captures a spectral image of a region of the substrate.

The imager of an embodiment is configured to capture a plurality of one-dimensional images from the reflected light of a pad-contacting surface of the substrate and to generate at least one two-dimensional image from the plurality of one-dimensional images.

The one-dimensional images of an embodiment represent at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.

The two-dimensional images of an embodiment include spectral images of at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.

The one-dimensional images of an embodiment comprise line images.

The at least one two-dimensional image of an embodiment is derived from data points. The data points are one or more of substantially contiguous and substantially non-contiguous points.

The imager of an embodiment includes a spatial dimension and a spectral dimension for receiving dissected light from the wavelength-dispersive element. The imager generates a two-dimensional data set for each of the one-dimensional images. A first dimension of the two-dimensional data set comprises a spatial dimension. A second dimension of the two-dimensional data set comprises a spectral dimension.

The imager of an embodiment further comprises a processor configured to derive a frame from the two-dimensional data set.

The system of an embodiment includes a spectrometer lens assembly configured to receive the reflected light from the substrate. The system of an embodiment includes a wavelength-dispersive element configured to receive light from the spectrometer lens assembly. The system of an embodiment includes an imager configured to receive light from the wavelength dispersive element, wherein the imager captures a spectral image of a region of the substrate.

The aperture of an embodiment has a dimension greater than a diameter of the substrate. The image includes an image of an entire surface of the substrate.

The aperture of an embodiment has a dimension approximately equal to a maximum planar dimension of a die of the substrate.

The aperture of an embodiment has a dimension less than a diameter of the substrate. The image includes an image of a die of the substrate and an area smaller than an entire surface of the substrate.

The system of an embodiment includes at least one motor coupled to rotate one or more of the platen and the carrier.

The polishing of an embodiment is chemical-mechanical planarization.

The polishing of an embodiment is orbital chemical-mechanical planarization. The polishing pad undergoes orbital motion about a center point aligned with a rotational axis of the substrate.

The substrate imaging of an embodiment includes a method comprising securing a substrate to a carrier and disposing a platen in a variety of positions relative to the substrate. The platen includes an aperture configured to pass light and a polishing pad. The method includes polishing the substrate with the polishing pad. The polishing includes illuminating the substrate by passing light through the aperture. The polishing also includes receiving reflected light from the substrate through the aperture. The polishing further includes imaging the substrate using information of the reflected light.

The method of an embodiment includes configuring the polishing pad to include an optical element that is positioned relative to the aperture to pass light to and from the aperture. The optical element of an embodiment is optically transparent.

The method of an embodiment includes passing the light to the aperture using a first set of optical fibers coupled to an illumination source.

The method of an embodiment includes passing the reflected light from the aperture using an optoelectronic system that includes an optical receiver coupled to the aperture.

The method of an embodiment includes dispersing the received light from the spectrometer lens assembly according to a wavelength of the received light.

The method of an embodiment includes capturing a spectral image of a region of the substrate from information of dispersed light.

The capturing of an embodiment includes capturing a plurality of one-dimensional images from the reflected light of a pad-contacting surface of the substrate and generating at least one two-dimensional image from the plurality of one-dimensional images.

The plurality of one-dimensional images of an embodiment represents at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.

The two-dimensional image of an embodiment includes spectral images of at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.

The method of an embodiment includes receiving dispersed light in a spatial dimension and a spectral dimension, and generating a two-dimensional data set for each of the one-dimensional images. A first dimension of the two-dimensional data set includes a spatial dimension. A second dimension of the two-dimensional data set includes a spectral dimension.

The method of an embodiment includes rotating one or more of the platen and the carrier.

The substrate imaging of an embodiment includes a system comprising a carrier holding a substrate, a platen holding a polishing pad, and a frame for disposing the platen relative to the carrier. The system also includes a reflectance image processing subsystem for acquiring one or more two-dimensional images of the substrate during CMP of the substrate and deriving from the images information about the substrate useful for subsequent CMP of the substrate.

The system of an embodiment includes a device for rotating the platen.

The reflectance image processing subsystem includes a device for capturing a number of one-dimensional reflectance images and deriving the one or more two-dimensional images from the one-dimensional reflectance images.

The substrate of an embodiment includes further comprises a pad-contacting surface.

The reflectance image processing subsystem includes a device for capturing a plurality of one-dimensional images from light reflected from the pad-contacting surface, and deriving the one or more two-dimensional images from the one-dimensional reflectance images.

The two-dimensional images of an embodiment includes comprise spectral images.

The two-dimensional images of an embodiment includes are derived from data points.

The data points of an embodiment are substantially contiguous.

The data points of an embodiment are substantially non-contiguous.

The substrate imaging of an embodiment includes a substrate imaging system comprising a carrier holding a substrate, the substrate having a pad-contacting surface, a platen holding a polishing pad, and a frame for operatively disposing the platen relative to the carrier. The system of an embodiment includes an image processing subsystem for capturing, from light reflected from the pad-contacting surface and transmitted through one or more optically transparent elements in the platen and/or polishing pad, a number of one-dimensional images representative of at least a portion of the pad-contacting surface of the substrate during traversal of the opening and/or optically transparent elements. The image processing subsystem derives from the one-dimensional images a frame comprising frame data providing information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

The one-dimensional images of an embodiment comprise line images.

The image processing subsystem of an embodiment comprises a light source. The image processing subsystem of an embodiment includes a first bundle of optical fibers carrying light from the light source to an aperture or slit in the platen. The image processing subsystem of an embodiment includes a second bundle of optical fibers carrying light reflected from the pad-contacting surface to a wavelength dispersive element for dissecting spatial components of the one-dimensional images into their respective wavelength components.

The image processing subsystem of an embodiment comprises a two-dimensional imager having a spatial dimension and a spectral dimension for receiving the dissected light from the wavelength dispersive element, and providing a two-dimensional collection of data for each of the one-dimensional images, a first dimension of the collection comprising a spatial dimension, and a second dimension of the collection comprising a spectral dimension, and a processor for deriving a frame from a plurality of the two-dimensional collections.

The optical fibers of an embodiment in the first and second bundles each have terminating ends arranged in a fiber assembly element fitted to an underside of the platen.

The terminating ends of the fibers of an embodiment are arranged in an arrangement in which terminating ends of fibers in the first bundle form first and second rows, and the terminating ends of fibers in the second bundle form a third row placed between the first and second rows.

The substrate imaging of an embodiment includes a system comprising a carrier holding a substrate that includes a pad-contacting surface with a maximum planar dimension. The system of an embodiment includes a platen having a radius and holding a polishing pad. The platen of an embodiment includes a slit having a length equal to or exceeding the maximum planar dimension of the substrate. The length of the slit of an embodiment is disposed substantially along the platen radius. The polishing pad of an embodiment includes an optically transparent element located at about the slit.

The system of an embodiment includes a frame for operatively disposing the platen relative to the carrier, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the slit when the pad-contacting surface moves relative to the platen.

The system of an embodiment includes an image processing subsystem for capturing, from light reflected from the pad-contacting surface and transmitted through the optically transparent element and the slit, a number of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the substrate during traversal of the pad-contacting surface past the slit, and deriving from the images a frame comprising frame data useful for subsequent chemical-mechanical processing of the substrate.

The system of an embodiment includes a device for rotating the platen.

The one-dimensional images of an embodiment comprise line images.

The image processing subsystem of an embodiment comprises a light source, a first bundle of optical fibers carrying light from the light source to the slit in the platen, and a second bundle of optical fibers carrying light reflected from the pad-contacting surface to a wavelength dispersive element for dissecting spatial components of the one-dimensional images into their respective wavelength components.

The image processing subsystem of an embodiment includes a two-dimensional imager having a spatial dimension and a spectral dimension for receiving dissected light from the wavelength dispersive element, and providing a two-dimensional collection of data for each of the one-dimensional images, a first dimension of the collection comprising a spatial dimension, and a second dimension of the collection comprising a spectral dimension, and a processor for deriving a frame from a plurality of two-dimensional collections.

The optical fibers in the first and second bundles of an embodiment each have terminating ends arranged in a fiber assembly element fitted to an underside of the platen.

The terminating ends of the fibers of an embodiment are configured so terminating ends of fibers in the first bundle form first and second rows, and terminating ends of fibers in the second bundle form a third row placed between the first and second rows.

The substrate imaging of an embodiment includes a system comprising a carrier holding a substrate with a pad-contacting surface forming a die and having a maximum planar dimension.

The system of an embodiment includes a rotating platen having a radius and holding a polishing pad. The platen of an embodiment includes a slit having a length approximately equal to the maximum planar dimension of the die. The aperture or slit length of an embodiment is disposed substantially along the platen radius. The polishing pad of an embodiment has an optically transparent element located at about the slit.

The system of an embodiment includes a frame for operatively disposing the rotating platen relative to the carrier, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the slit within a rotation of the platen.

The system of an embodiment includes an image processing subsystem for capturing, from light reflected from the pad-contacting surface and transmitted through the optically transparent element and the slit, a number of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the die during traversal of the pad-contacting surface past the slit, and deriving from the images a frame comprising frame data providing information about the die useful for subsequent chemical-mechanical processing of the substrate.

The image processing subsystem of an embodiment comprises a light source, a first bundle of optical fibers carrying light from the light source to the slit in the platen, and a second bundle of optical fibers carrying light reflected from the pad-contacting surface to a wavelength dispersive element for dissecting spatial components of the one-dimensional images into their respective wavelength components.

The image processing subsystem of an embodiment includes a two-dimensional imager having a spatial dimension and a spectral dimension for receiving dissected light from the wavelength dispersive element, and providing a two-dimensional collection of data for each of the one-dimensional images. A first dimension of the collection includes a spatial dimension. A second dimension of the collection includes a spectral dimension. The image processing subsystem of an embodiment includes a processor for deriving a frame from the two-dimensional collections.

The optical fibers in the first and second bundles of an embodiment each have terminating ends arranged in a fiber assembly element fitted to an underside of the platen.

The terminating ends of the fibers of an embodiment are arranged in an arrangement in which terminating ends of fibers in the first bundle form first and second rows, and the terminating ends of fibers in the second bundle form a third row placed between the first and second rows.

The substrate imaging of an embodiment includes a system for imaging a substrate during CMP. The system of an embodiment includes a carrier holding a substrate, the substrate having a pad-contacting surface, a rotating platen holding a polishing pad, and a frame for operatively disposing the rotating platen relative to the carrier. The system of an embodiment includes an image processing subsystem for capturing, from light reflected from the pad-contacting surface and transmitted through one or more optically transparent elements in the platen and/or polishing pad, data points representative of at least a portion of the pad-contacting surface of the substrate during traversal of the opening and/or optically transparent elements. The system of an embodiment is configured to derive from the data points one or more one-dimensional reflectance images of a portion of a substrate, where data point spacing is determined by an array of data collection locations disposed substantially non-parallel to the direction of substrate motion.

The data points used for deriving the one or more images of an embodiment are substantially contiguous.

The data points used for deriving the one or more images of an embodiment are substantially non-contiguous.

The one or more images of an embodiment are spectral images.

The image processing subsystem of an embodiment aggregates the one-dimensional images to form a two-dimensional image of the substrate. The two-dimensional image provides information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

The image processing subsystem of an embodiment forms one or more two-dimensional images of at least a portion of the substrate.

The substrate imaging of an embodiment includes a method for polishing a semiconductor substrate. The method of an embodiment includes acquiring one or more two-dimensional images of the substrate during CMP, and deriving from the images information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

The derived information of an embodiment comprises frame data suitable for reproducing the one or more two-dimensional images.

A two dimensional image of an embodiment comprises a number of one-dimensional images, each one-dimensional image reflected from a different portion of the substrate.

The two-dimensional images of an embodiment comprise spectral images.

The substrate imaging of an embodiment includes a method of imaging a substrate comprising one or more of holding a substrate having a pad-contacting surface, holding a polishing pad with a platen including one or more optically transparent elements, operatively disposing the rotating platen relative to the pad-contacting surface, such that the pad-contacting surface contacts the polishing pad, and substantially completely traverses the one or more optically transparent elements within a rotation of the platen, capturing, from light reflected from the pad-contacting surface and transmitted through the one or more optically transparent elements, a plurality of one-dimensional images representative of at least a portion of the pad-contacting surface during traversal of the pad-contacting surface past the optically transparent elements, and deriving from data of the images a frame comprising frame data useful for subsequent chemical-mechanical processing of the substrate.

The capturing of an embodiment comprises one or more of carrying light from a light source to the optically transparent elements in the platen, carrying light reflected from the pad-contacting surface to a wavelength dispersive element, and dissecting spatial components of the one-dimensional images into their respective wavelength components.

The capturing of an embodiment comprises one or more of receiving, at a two-dimensional imager having a spatial dimension and a spectral dimension, dissected light from the wavelength dispersive element, and providing a two-dimensional collection of data for each of the one-dimensional images, a first dimension of the collection comprising a spatial dimension, and a second dimension of the collection comprising a spectral dimension.

The deriving of an embodiment comprises deriving a frame from a number of the two-dimensional collections.

The substrate imaging of an embodiment includes a method for acquiring a two-dimensional image of a substrate during CMP, comprising one or more of holding a substrate, the substrate having a pad-contacting surface and a maximum planar dimension, holding a polishing pad with a rotating platen, the platen having a radius and including a slit having a length disposed substantially along the radius of the platen and equal to or exceeding the maximum planar dimension of the substrate, the platen also including an optically transparent element located at about the slit, operatively disposing the rotating platen relative to the pad-contacting surface, such that the pad-contacting surface of the substrate contacts the polishing pad, and substantially completely traverses the slit within a rotation of the platen, capturing, from light reflected from the pad-contacting surface and transmitted through the optically transparent element, a plurality of one-dimensional images representative of the substantial entirety of the pad-contacting surface of the substrate during traversal of the pad-contacting surface past the slit, and deriving from the images a frame comprising frame data providing information about the substrate useful for subsequent chemical-mechanical processing of the substrate.

The capturing of an embodiment comprises one or more of carrying light from a light source to the slit in the platen, carrying light reflected from the pad-contacting surface to a wavelength dispersive element, and dissecting spatial components of the one-dimensional images into their respective wavelength components.

The capturing of an embodiment comprises one or more of receiving, at a two-dimensional imager having a spatial dimension and a spectral dimension, dissected light from the wavelength dispersive element, and providing a two-dimensional collection of data for each of the one-dimensional images, a first dimension of the collection comprising a spatial dimension, and a second dimension of the collection comprising a spectral dimension.

The substrate imaging of an embodiment includes a substrate imaging system, comprising a carrier holding a substrate, a pad structure holding a polishing pad, and a frame for disposing the platen relative to the carrier. The system of an embodiment includes a reflectance image processing subsystem for acquiring one or more two-dimensional images of the substrate during CMP of the substrate and deriving from the images information about the substrate useful for subsequent CMP of the substrate.

The system of an embodiment rotates the carrier.

The system of an embodiment orbits the pad structure.

The reflectance image processing subsystem of an embodiment comprises a device for capturing a number of one-dimensional reflectance images and deriving one or more two-dimensional images from the one-dimensional images.

The substrate of an embodiment comprises a pad-contacting surface.

The reflectance image processing subsystem of an embodiment includes a device for capturing a number of one-dimensional images from light reflected from the pad-contacting surface, and deriving the one or more two-dimensional images from the one-dimensional images.

The two-dimensional images of an embodiment represent a portion of the substrate. The portion of an embodiment can be annular shaped. The portion of an embodiment can be disc shaped. The portion of an embodiment can include the substrate substantially in its entirety.

As utilized herein, terms such as “about” and “substantially” and “near” are intended to allow some leeway in mathematical exactness to account for tolerances that are acceptable in the trade. Accordingly, any deviations upward or downward from the value modified by the terms “about” or “substantially” or “near” in the range of 1% to 20% should be considered to be explicitly within the scope of the stated value.

As used herein, the term “software” includes source code, assembly language code, binary code, firmware, macro-instructions, micro-instructions, or the like, or any combination of two or more of the foregoing. The term “memory” refers to any processor-readable medium, including but not limited to RAM, ROM, EPROM, PROM, EEPROM, disk, floppy disk, hard disk, CD-ROM, DVD, or the like, or any combination of two or more of the foregoing, on which may be stored a series of software instructions executable by a processor.

The terms “processor” or “CPU” refer to any device capable of executing a series of instructions and includes, without limitation, a general- or special-purpose microprocessor, finite state machine, controller, computer, digital signal processor (DSP), or the like. The term “logic” refers to embodiments in hardware, software, or combinations of hardware and software.

The term “CMP” means chemical mechanical planarization, or, more generally, any chemical mechanical processing performed on a semiconductor substrate.

Aspects of the imaging described herein may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (PLDs), such as field programmable gate arrays (FPGAs), programmable array logic (PAL) devices, electrically programmable logic and memory devices and standard cell-based devices, as well as application specific integrated circuits (ASICs). Some other possibilities for implementing aspects of the imaging include: microcontrollers with memory (such as electronically erasable programmable read only memory (EEPROM)), embedded microprocessors, firmware, software, etc. Furthermore, aspects of the imaging may be embodied in microprocessors having software-based circuit emulation, discrete logic (sequential and combinatorial), custom devices, fuzzy (neural) logic, quantum devices, and hybrids of any of the above device types. Of course the underlying device technologies may be provided in a variety of component types, e.g., metal-oxide semiconductor field-effect transistor (MOSFET) technologies like complementary metal-oxide semiconductor (CMOS), bipolar technologies like emitter-coupled logic (ECL), polymer technologies (e.g., silicon-conjugated polymer and metal-conjugated polymer-metal structures), mixed analog and digital, etc.

It should be noted that the various components disclosed herein may be described and expressed (or represented) as data and/or instructions embodied in various computer-readable media. Computer-readable media in which such data and/or instructions may be embodied include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media) and carrier waves that may be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media or any combination thereof. Examples of transfers of such data and/or instructions by carrier waves include, but are not limited to, transfers (uploads, downloads, e-mail, etc.) over the Internet and/or other computer networks via one or more data transfer protocols (e.g., HTTP, FTP, SMTP, etc.). When received within a computer system via one or more computer-readable media, such data and/or instruction-based expressions of the above described components may be processed by a processing entity (e.g., one or more processors) within the computer system in conjunction with execution of one or more other computer programs.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of “including, but not limited to.” Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words “herein,” “hereunder,” “above,” “below,” and words of similar import refer to this application as a whole and not to any particular portions of this application. When the word “or” is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.

The above description of illustrated embodiments of the imaging is not intended to be exhaustive or to limit the imaging to the precise form disclosed. While specific embodiments of, and examples for, the imaging are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the imaging, as those skilled in the relevant art will recognize. The teachings of the imaging provided herein can be applied to other processing systems and methods, not only for the systems and methods described above.

The elements and acts of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the imaging in light of the above detailed description.

In general, in the following claims, the terms used should not be construed to limit the imaging to the specific embodiments disclosed in the specification and the claims, but should be construed to include all processing systems that operate under the claims. Accordingly, the imaging is not limited by the disclosure, but instead the scope of the imaging is to be determined entirely by the claims.

While certain aspects of the imaging are presented below in certain claim forms, the inventors contemplate the various aspects of the imaging in any number of claim forms. For example, while only one aspect of the imaging is recited as embodied in machine-readable medium, other aspects may likewise be embodied in machine-readable medium. Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the imaging. 

1. A system comprising: a carrier configured to receive a substrate; a platen that includes an aperture configured to pass light, wherein the platen is configured to receive a polishing pad; a frame that disposes the platen in a plurality of positions relative to the carrier; an optoelectronic system coupled to the aperture, wherein the aperture passes light of the optoelectronic system to illuminate the substrate and passes reflected light from the substrate to the optoelectronic system; and a processing system that uses the reflected light to image the substrate as the polishing pad is polishing the substrate.
 2. The system of claim 1, wherein the polishing pad includes an optical element that is positioned relative to the aperture to pass light to and from the aperture, wherein the optical element is optically transparent.
 3. The system of claim 1, wherein the optoelectronic system includes an illumination source coupled to the aperture.
 4. The system of claim 3, further comprising a first set of optical fibers coupled to the illumination source and the aperture.
 5. The system of claim 1, wherein the optoelectronic system includes an optical receiver coupled to the aperture, the optical receiver configured to receive the reflected light.
 6. The system of claim 5, wherein the optical receiver is a second set of optical fibers.
 7. The system of claim 5, wherein the optical receiver includes one or more of a receiver lens assembly and a receiver aperture.
 8. The system of claim 5, wherein the optical receiver includes a receiver aperture.
 9. The system of claim 5, further comprising a spectrometer lens assembly configured to receive light from the optical receiver.
 10. The system of claim 9, further comprising: a wavelength-dispersive element configured to receive light from the spectrometer lens assembly; and an imager configured to receive light from the wavelength dispersive element, wherein the imager captures a spectral image of a region of the substrate.
 11. The system of claim 10, wherein the imager is configured to capture a plurality of one-dimensional images from the reflected light of a pad-contacting surface of the substrate and to generate at least one two-dimensional image from the plurality of one-dimensional images.
 12. The system of claim 11, wherein the plurality of one-dimensional images represent at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.
 13. The system of claim 11, wherein the two-dimensional image includes spectral images of at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.
 14. The system of claim 11, wherein the one-dimensional images comprise line images.
 15. The system of claim 11, wherein the at least one two-dimensional image is derived from data points, wherein the data points are one or more of substantially contiguous and substantially non-contiguous.
 16. The system of claim 10, wherein the imager includes a spatial dimension and a spectral dimension for receiving dissected light from the wavelength-dispersive element, wherein the imager generates a two-dimensional data set for each of the one-dimensional images, a first dimension of the two-dimensional data set comprising a spatial dimension, and a second dimension of the two-dimensional data set comprising a spectral dimension.
 17. The system of claim 16, wherein the imager further comprises a processor configured to derive a frame from the two-dimensional data set.
 18. The system of claim 1, further comprising one or more of a spectrometer lens assembly configured to receive the reflected light from the substrate and a wavelength-dispersive element configured to receive light from the spectrometer lens assembly, and an imager configured to receive light from the wavelength dispersive element, wherein the imager captures a spectral image of a region of the substrate.
 19. The system of claim 1, wherein the aperture has a dimension greater than a diameter of the substrate, wherein the image includes an image of an entire surface of the substrate.
 20. The system of claim 1, wherein the aperture has a dimension approximately equal to a maximum planar dimension of a die of the substrate.
 21. The system of claim 1, wherein the aperture has a dimension less than a diameter of the substrate, wherein the image includes an image of a die of the substrate and an area smaller than an entire surface of the substrate.
 22. The system of claim 1, further comprising at least one motor coupled to rotate one or more of the platen and the carrier.
 23. The system of claim 1, wherein the polishing is chemical-mechanical planarization.
 24. The system of claim 1, wherein the polishing is orbital chemical-mechanical planarization, wherein the polishing pad undergoes orbital motion about a center point aligned with a rotational axis of the substrate.
 25. A method comprising: securing a substrate to a carrier; disposing a platen in a plurality of positions relative to the substrate, wherein the platen includes an aperture configured to pass light and a polishing pad; and polishing the substrate with the polishing pad, the polishing including illuminating the substrate by passing light through the aperture, the polishing further including receiving reflected light from the substrate through the aperture, the polishing further including imaging the substrate using information of the reflected light.
 26. The method of claim 25, further comprising configuring the polishing pad to include an optical element that is positioned relative to the aperture to pass light to and from the aperture, wherein the optical element is optically transparent.
 27. The method of claim 25, further comprising passing the light to the aperture using a first set of optical fibers coupled to an illumination source.
 28. The method of claim 25, further comprising passing the reflected light from the aperture using an optoelectronic system that includes an optical receiver coupled to the aperture.
 29. The method of claim 28, wherein the optical receiver is a second set of optical fibers.
 30. The method of claim 28, wherein the optical receiver includes one or more of a receiver lens assembly and a receiver aperture.
 31. The method of claim 28, wherein the optical receiver includes a receiver aperture.
 32. The method of claim 28, further comprising a spectrometer lens assembly configured to receive light from the optical receiver.
 33. The method of claim 32, further comprising: dispersing the received light from the spectrometer lens assembly according to a wavelength of the received light; and capturing a spectral image of a region of the substrate from information of dispersed light.
 34. The method of claim 33, wherein the capturing includes capturing a plurality of one-dimensional images from the reflected light of a pad-contacting surface of the substrate and generating at least one two-dimensional image from the plurality of one-dimensional images.
 35. The method of claim 34, wherein the plurality of one-dimensional images represent at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.
 36. The method of claim 34, wherein the two-dimensional image includes spectral images of at least a portion of a pad-contacting surface of the substrate during traversal of the aperture.
 37. The method of claim 33, further comprising receiving dispersed light in a spatial dimension and a spectral dimension, and generating a two-dimensional data set for each of the one-dimensional images, a first dimension of the two-dimensional data set comprising a spatial dimension, and a second dimension of the two-dimensional data set comprising a spectral dimension.
 38. The method of claim 25, wherein the aperture has a dimension that is one of greater than a diameter of the substrate, approximately equal to a maximum planar dimension of a die of the substrate, and less than a diameter of the substrate.
 39. The method of claim 25, further comprising rotating one or more of the platen and the carrier.
 40. The method of claim 25, wherein the polishing is chemical-mechanical planarization.
 41. The method of claim 25, wherein the polishing is orbital chemical-mechanical planarization. 